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mahjongg2 / ZX81plus38

Mij latest ZX81 clone without ULA built from discrete pin through hole components
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ZX80 compatibility #1

Open stevexyz opened 4 years ago

stevexyz commented 4 years ago

Does it work also as a ZX80? Here you can see a nice trick that will do with 4 resistors in case! https://sinclairzxworld.com/viewtopic.php?t=1329

mahjongg2 commented 4 years ago

Never tried to run Z80 software on a ZX81, but I see no reason why it couldn’t work, if you use a ZX80 ROM, and add the pull down resistors, just try it!

let me know how it went...

Op 29 jun. 2020, om 21:39 heeft Stefano notifications@github.com het volgende geschreven:

Does it work also as a ZX80? Here you can see a nice trick that will do with 4 resistors in case! https://sinclairzxworld.com/viewtopic.php?t=1329 https://sinclairzxworld.com/viewtopic.php?t=1329 — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub https://github.com/mahjongg2/ZX81plus38/issues/1, or unsubscribe https://github.com/notifications/unsubscribe-auth/ACAHA4AEGFD2F7OQY7AV7R3RZDUY5ANCNFSM4OLQ5RKQ.

stevexyz commented 4 years ago

It was a suggestion to avoid to have a post modding in case, and from what I've understood then just switching the ROM would be enough.

Native ZX80 compatibility (an interesting machine on itself) would be surely a plus of this nice board, and your discrete logic approach is very similar to ZX80 philosophy!

mahjongg2 commented 4 years ago

I have not investigated what exactly the four pulldown resistors do, and I also fail to see what effect they would have on the Z80’s behaviour before reset. If I understand the trick they somehow disable the initial NMI the z80 might see so that the software gets a chance to disable NMI’s before being forced into the NMI vector.

Don’t understand how that would work, and I would need conformation it does before adding new hardware to either the ZX81+35 or ZX81+38.

Especially the ZX81+35 is a closed chapter for me, as it was developed on an ancient laptop I hope I would never have to start up again.

Just had to create a new set of production files for the ZX81+35, and it was a very painful process.

Op 29 jun. 2020, om 21:39 heeft Stefano notifications@github.com het volgende geschreven:

Does it work also as a ZX80? Here you can see a nice trick that will do with 4 resistors in case! https://sinclairzxworld.com/viewtopic.php?t=1329 https://sinclairzxworld.com/viewtopic.php?t=1329 — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub https://github.com/mahjongg2/ZX81plus38/issues/1, or unsubscribe https://github.com/notifications/unsubscribe-auth/ACAHA4AEGFD2F7OQY7AV7R3RZDUY5ANCNFSM4OLQ5RKQ.

stevexyz commented 3 years ago

My suggestion was here for the plus38, that I consider a real beauty!

If the described change was working (I've anyway no possibility to test it but seems someone did) I was thinking of a jumper or a switch to switch ROM and in case other required circuit parts if needed, to have both the two computers into one (and the ZX80 is by far the fastest in basic ;))

Either way (with or without ZX80 compatibility) when you'll finish I want to try to build one for myself! :)

stevexyz commented 3 years ago

The readme update states: "The use of a 4K ZX80 ROM is also supported", it means plus38 is working as a ZX80 even without hw changes (meaning just changing ROM)?

mahjongg2 commented 3 years ago

No that comment was only made because a ZX80 ROM has a different pinout than a ZX81 ROM, (it has less pins) but I have added jumpers so that a real (26pin-pin) ZX80 rom would technically work in a ZX81+38 (its jumpering can be changed so that the smaller ZX80 ROM can get power and data/address/control lines on the correct pins with some simple patches.

It does NOT mean the ZX80 rom will just work, I have not tried that yet, and on the ZX81+35 the ROM socket is for a QFP chip, so its not physically possible to put in a real ZX80 ROM

mahjongg2 commented 3 years ago

P.S. I have read the post that stated that you could Disable NMI even before any code runs by adding four pulldown resistors, and I see no reason why that trick would not work on my clone also, but that said "the proof of the pudding is in the eating", so it has to be tried out.

I do want to make one remark though, and that is that the ZX81 (and thus my clone also) has weak pullups on the databus so that when the ZX80 does an IORD to determine the presence of a connected ZXPrinter it can detect its absence reliably, because it will read a 0xFF instead of whatever the ZXPrinter puts on the bus when its present. The above patch might interfere with this patch by pulling one data bit low instead of high.

dkknab commented 3 years ago

Got your zx81/80 board going tonight. Used 12mhz crystal though it wouldn't start consistently. Also used ZX80 rom loaded on AT28C256 making the changes per the board. Couldn't get ZX81 rom to work... not sure why though it may be due to the lower crystal. Also couldn't get it to load from WAV files from phone on first try using ZX80 ROM.

mahjongg2 commented 3 years ago

Nice!

Do you have the latest PCB, if not it needs patches for slow mode!

To be hones, I have still not built my own board, as I’m quite disabled due to lockdown, my asthma has become crippling, and I’m very tired always. I found all the parts, I have the PCB,. and a simple but suitable soldering iron, but Revspace is completely closed, so I can go there. I’m hoping to recover and get my strength back.

I’m wondering why the ZX81 rom doesn’t work, but that it works as a ZX80 is good news, I wasn’t certain of that.

Did you put the same code in the 16K ROM twice?. it needs that to be like an 8K ROM!

There is quite some activity round the ZX81 as many people are celebrating its 40th anniversary. I’m replaying to some posts with a link to my GitHub and revspace posts.

a 13MHz xtal should be necessary, as 12MHz, is quite far off for correct video timing! Farnell should have one!, also loading and saving can be affected, especially if you load original games and such.

keep trying, did you visit the german forum (if you can read German, I can) you can find it here: So sieht meine ZX81-Klonplatine aus https://forum.tlienhard.com/phpBB3/viewtopic.php?f=2&t=3266 various persons have gotten my ZX-81+38 to work, after these people found a few hardware bugs, I have made the changes.

there is also an english language discussion group discussing the ZX81+38, here: I started on my new ZX-81 replacement board (kit) ZX81+38 https://www.sinclairzxworld.com/viewtopic.php?p=35160#p35160

Good luck!

Op 5 mrt. 2021, om 18:05 heeft dkknab notifications@github.com het volgende geschreven:

Got your zx81/80 board going tonight. Used 12mhz crystal though it wouldn't start consistently. Also used ZX80 rom loaded on AT28C256 making the changes per the board. Couldn't get ZX81 rom to work... not sure why though it may be due to the lower crystal. Also couldn't get it to load from WAV files from phone on first try using ZX80 ROM.

— You are receiving this because you commented. Reply to this email directly, view it on GitHub https://github.com/mahjongg2/ZX81plus38/issues/1#issuecomment-791553664, or unsubscribe https://github.com/notifications/unsubscribe-auth/ACAHA4ARZNIC3BW43AKIBYLTCEFPPANCNFSM4OLQ5RKQ.

dkknab commented 3 years ago

Thanks for the response. Let me see if I can share what I've done in response to your questions. I will start by saying I am a complete novice. I started with Ben Eater's 6502 project and have taken off from there making 6502 boards and Z80 boards.

First off I am using the REV 1.6 board...the last one I believe you posted. I got some from PCBway and JLCPCB. I'm not sure at all what you mean by the patches for slow mode as I'm guessing it does not apply to REV1.6

I do have some extra boards - this was the first time I ordered a PCB so I ordered some from PCBWay and JLCPCB. I have 10 boards in all so if you know someone who needs one I can share it with them if that's ok with you.

Sorry to hear you are not 100%. I know for me working on these projects is a distraction. I hope you get well soon!

I was thinking the reason the ZX81 rom doesn’t work is because of the crystal. Once I get a 13mhz crystal I'll try the ZX81 rom again. It's neat with the ZX80. I made the keyboard pictured on github. I didn't realize the ZX80 keyboard is slightly different than the ZX81. I have two of the TIMEX Sinclair 1000s that I've been messing with too.

I am using the AT28C256 eeprom which is 32K I believe. I only put in the ZX81 code once. I'll have to load it a few times. Where do I start the subsequent images of the code on the eeprom? Do I put it at 0K, then 8K, 16K and finally 24K locations?

I was completely surprised too that the 12MHz crystal works for the ZX80. At least I know the board works just fine. I have ordered the 13mhz crystal's from Mouser here in the US -I haven't tried to order from Farnell. Where are they located?

AS I mentioned too I can't load from a audio file so the fact I have the 12mhz crsytal must be impacting that too.

I will keep trying. I do not read or speak German but maybe through the wonder of the internet it will translate it for me. I'll be sure to check it out as well as the english version of the discussion group you mentioned.

I'll let you know how things go especially when I get the new crystal and if I have any luck with the ZX81 rom. Thanks for doing this! David Knab

On Fri, Mar 5, 2021 at 12:38 PM mahjongg2 notifications@github.com wrote:

Nice!

Do you have the latest PCB, if not it needs patches for slow mode!

To be hones, I have still not built my own board, as I’m quite disabled due to lockdown, my asthma has become crippling, and I’m very tired always. I found all the parts, I have the PCB,. and a simple but suitable soldering iron, but Revspace is completely closed, so I can go there. I’m hoping to recover and get my strength back.

I’m wondering why the ZX81 rom doesn’t work, but that it works as a ZX80 is good news, I wasn’t certain of that.

Did you put the same code in the 16K ROM twice?. it needs that to be like an 8K ROM!

There is quite some activity round the ZX81 as many people are celebrating its 40th anniversary. I’m replaying to some posts with a link to my GitHub and revspace posts.

a 13MHz xtal should be necessary, as 12MHz, is quite far off for correct video timing! Farnell should have one!, also loading and saving can be affected, especially if you load original games and such.

keep trying, did you visit the german forum (if you can read German, I can) you can find it here: So sieht meine ZX81-Klonplatine aus < https://forum.tlienhard.com/phpBB3/viewtopic.php?f=2&t=3266> various persons have gotten my ZX-81+38 to work, after these people found a few hardware bugs, I have made the changes.

there is also an english language discussion group discussing the ZX81+38, here: I started on my new ZX-81 replacement board (kit) ZX81+38 < https://www.sinclairzxworld.com/viewtopic.php?p=35160#p35160>

Good luck!

Op 5 mrt. 2021, om 18:05 heeft dkknab notifications@github.com het volgende geschreven:

Got your zx81/80 board going tonight. Used 12mhz crystal though it wouldn't start consistently. Also used ZX80 rom loaded on AT28C256 making the changes per the board. Couldn't get ZX81 rom to work... not sure why though it may be due to the lower crystal. Also couldn't get it to load from WAV files from phone on first try using ZX80 ROM.

— You are receiving this because you commented. Reply to this email directly, view it on GitHub < https://github.com/mahjongg2/ZX81plus38/issues/1#issuecomment-791553664>, or unsubscribe < https://github.com/notifications/unsubscribe-auth/ACAHA4ARZNIC3BW43AKIBYLTCEFPPANCNFSM4OLQ5RKQ .

— You are receiving this because you commented. Reply to this email directly, view it on GitHub https://github.com/mahjongg2/ZX81plus38/issues/1#issuecomment-791573565, or unsubscribe https://github.com/notifications/unsubscribe-auth/ASNSXJD3G3NNDXQGKTL2VCLTCEJJPANCNFSM4OLQ5RKQ .

mahjongg2 commented 3 years ago

Dear David,

First I’m located in the Netherlands and yes, the revision 1.6 Board is the latest, (in march 2021) and should work fine, according to both the English and german forums, you can translate the german texts using copy/paste, and the google translate site.

I’m a bit shocked that 12MHz generates a good picture, I know that the original 6.5 Mhz resonators are not very precise, but 6 and 6.5 MHz, that is eight percent or so difference, and TV’s are very finicky about timing, even for a black and white signal.

I have been gifted a 1.6 PCB, so I have one, and a few older (1.4) versions too) I could patch up.

did you check the jumping for the AT28C256 (OTP) rom, as there are several jumpers that can be changed for older ROM’s, but AFAIK the default should be good for 32K ROM’s, and yes, I always put multiple copies, at 8K borders in, just so that there is less chance you put the 8K image at the wrong location in ROM, and yes at 8K borders, so 0K 8K 16K and 24K

I’m thinking about designing a specific keyboard PCB for the ZX81+38 too, although the ZX81+34 compatible keyboard works works fine.

Farnell has a website and operates worldwide.

best regards, Martin de Jong (mahjongg)

Op 5 mrt. 2021, om 18:57 heeft dkknab notifications@github.com het volgende geschreven:

Thanks for the response. Let me see if I can share what I've done in response to your questions. I will start by saying I am a complete novice. I started with Ben Eater's 6502 project and have taken off from there making 6502 boards and Z80 boards.

First off I am using the REV 1.6 board...the last one I believe you posted. I got some from PCBway and JLCPCB. I'm not sure at all what you mean by the patches for slow mode as I'm guessing it does not apply to REV1.6

I do have some extra boards - this was the first time I ordered a PCB so I ordered some from PCBWay and JLCPCB. I have 10 boards in all so if you know someone who needs one I can share it with them if that's ok with you.

Sorry to hear you are not 100%. I know for me working on these projects is a distraction. I hope you get well soon!

I was thinking the reason the ZX81 rom doesn’t work is because of the crystal. Once I get a 13mhz crystal I'll try the ZX81 rom again. It's neat with the ZX80. I made the keyboard pictured on github. I didn't realize the ZX80 keyboard is slightly different than the ZX81. I have two of the TIMEX Sinclair 1000s that I've been messing with too.

I am using the AT28C256 eeprom which is 32K I believe. I only put in the ZX81 code once. I'll have to load it a few times. Where do I start the subsequent images of the code on the eeprom? Do I put it at 0K, then 8K, 16K and finally 24K locations?

I was completely surprised too that the 12MHz crystal works for the ZX80. At least I know the board works just fine. I have ordered the 13mhz crystal's from Mouser here in the US -I haven't tried to order from Farnell. Where are they located?

AS I mentioned too I can't load from a audio file so the fact I have the 12mhz crsytal must be impacting that too.

I will keep trying. I do not read or speak German but maybe through the wonder of the internet it will translate it for me. I'll be sure to check it out as well as the english version of the discussion group you mentioned.

I'll let you know how things go especially when I get the new crystal and if I have any luck with the ZX81 rom. Thanks for doing this! David Knab

On Fri, Mar 5, 2021 at 12:38 PM mahjongg2 notifications@github.com wrote:

Nice!

Do you have the latest PCB, if not it needs patches for slow mode!

To be hones, I have still not built my own board, as I’m quite disabled due to lockdown, my asthma has become crippling, and I’m very tired always. I found all the parts, I have the PCB,. and a simple but suitable soldering iron, but Revspace is completely closed, so I can go there. I’m hoping to recover and get my strength back.

I’m wondering why the ZX81 rom doesn’t work, but that it works as a ZX80 is good news, I wasn’t certain of that.

Did you put the same code in the 16K ROM twice?. it needs that to be like an 8K ROM!

There is quite some activity round the ZX81 as many people are celebrating its 40th anniversary. I’m replaying to some posts with a link to my GitHub and revspace posts.

a 13MHz xtal should be necessary, as 12MHz, is quite far off for correct video timing! Farnell should have one!, also loading and saving can be affected, especially if you load original games and such.

keep trying, did you visit the german forum (if you can read German, I can) you can find it here: So sieht meine ZX81-Klonplatine aus < https://forum.tlienhard.com/phpBB3/viewtopic.php?f=2&t=3266> various persons have gotten my ZX-81+38 to work, after these people found a few hardware bugs, I have made the changes.

there is also an english language discussion group discussing the ZX81+38, here: I started on my new ZX-81 replacement board (kit) ZX81+38 < https://www.sinclairzxworld.com/viewtopic.php?p=35160#p35160>

Good luck!

Op 5 mrt. 2021, om 18:05 heeft dkknab notifications@github.com het volgende geschreven:

Got your zx81/80 board going tonight. Used 12mhz crystal though it wouldn't start consistently. Also used ZX80 rom loaded on AT28C256 making the changes per the board. Couldn't get ZX81 rom to work... not sure why though it may be due to the lower crystal. Also couldn't get it to load from WAV files from phone on first try using ZX80 ROM.

— You are receiving this because you commented. Reply to this email directly, view it on GitHub < https://github.com/mahjongg2/ZX81plus38/issues/1#issuecomment-791553664>, or unsubscribe < https://github.com/notifications/unsubscribe-auth/ACAHA4ARZNIC3BW43AKIBYLTCEFPPANCNFSM4OLQ5RKQ .

— You are receiving this because you commented. Reply to this email directly, view it on GitHub https://github.com/mahjongg2/ZX81plus38/issues/1#issuecomment-791573565, or unsubscribe https://github.com/notifications/unsubscribe-auth/ASNSXJD3G3NNDXQGKTL2VCLTCEJJPANCNFSM4OLQ5RKQ .

— You are receiving this because you commented. Reply to this email directly, view it on GitHub https://github.com/mahjongg2/ZX81plus38/issues/1#issuecomment-791584010, or unsubscribe https://github.com/notifications/unsubscribe-auth/ACAHA4FEL4WML3QGLRFLHZ3TCELQBANCNFSM4OLQ5RKQ.

dkknab commented 3 years ago

For the Atmel AT28C256 rom, I did have to cut the trace on the underside for pin 1. And I placed the jumper JP10 I believe correctly. It may just be me but I was struggling with how to set the jumpers because I couldn't tell which pin is pin 1. Is it always the left pin when you read the text properly?

The other jumper I set was JP11 as per your schematics too.

JP4 is also set for 60hz. I too was surprised 12mhz worked. So does 12.288mhz but not on the first boot. I have to restart it a few times for it to catch.

I'm not using only older roms. I like the fact that your board is made up of readily available items. That's what makes this so much easier and fun. I'm trying to build the VIC2020... you may have seen this online. The problem there is you still need the VIC chip. The fact that you got rid of the ULA was a real enticement for me to do your board.

Take care

David Knab

On Fri, Mar 5, 2021, 1:21 PM mahjongg2 notifications@github.com wrote:

Dear David,

First I’m located in the Netherlands and yes, the revision 1.6 Board is the latest, and should work fine, according to both the English and german forums, you can translate the german texts using copy/paste, and the google translate site.

I’m a bit shocked that 12MHz generates a good picture, I know that the original 6.5 Mhz resonators are not very precise, but 6 and 6.5 MHz, that is eight percent or so difference, and TV’s are very finicky about timing, even for a black and white signal.

I have been gifted a 1.6 PCB, so I have one, and a few older (1.4) versions too) I could patch up.

did you check the jumping for the AT28C256 (OTP) rom, as there are several jumpers that can be changed for older ROM’s, but AFAIK the default should be good for 32K ROM’s, and yes, I always put multiple copies, at 8K borders in, just so that there is less chance you put the 8K image at the wrong location in ROM, and yes at 8K borders, so 0K 8K 16K and 24K

I’m thinking about designing a specific keyboard PCB for the ZX81+38 too, although the ZX81+34 compatible keyboard works works fine.

Farnell has a website and operates worldwide.

best regards, Martin de Jong (mahjongg)

Op 5 mrt. 2021, om 18:57 heeft dkknab notifications@github.com het volgende geschreven:

Thanks for the response. Let me see if I can share what I've done in response to your questions. I will start by saying I am a complete novice. I started with Ben Eater's 6502 project and have taken off from there making 6502 boards and Z80 boards.

First off I am using the REV 1.6 board...the last one I believe you posted. I got some from PCBway and JLCPCB. I'm not sure at all what you mean by the patches for slow mode as I'm guessing it does not apply to REV1.6

I do have some extra boards - this was the first time I ordered a PCB so I ordered some from PCBWay and JLCPCB. I have 10 boards in all so if you know someone who needs one I can share it with them if that's ok with you.

Sorry to hear you are not 100%. I know for me working on these projects is a distraction. I hope you get well soon!

I was thinking the reason the ZX81 rom doesn’t work is because of the crystal. Once I get a 13mhz crystal I'll try the ZX81 rom again. It's neat with the ZX80. I made the keyboard pictured on github. I didn't realize the ZX80 keyboard is slightly different than the ZX81. I have two of the TIMEX Sinclair 1000s that I've been messing with too.

I am using the AT28C256 eeprom which is 32K I believe. I only put in the ZX81 code once. I'll have to load it a few times. Where do I start the subsequent images of the code on the eeprom? Do I put it at 0K, then 8K, 16K and finally 24K locations?

I was completely surprised too that the 12MHz crystal works for the ZX80. At least I know the board works just fine. I have ordered the 13mhz crystal's from Mouser here in the US -I haven't tried to order from Farnell. Where are they located?

AS I mentioned too I can't load from a audio file so the fact I have the 12mhz crsytal must be impacting that too.

I will keep trying. I do not read or speak German but maybe through the wonder of the internet it will translate it for me. I'll be sure to check it out as well as the english version of the discussion group you mentioned.

I'll let you know how things go especially when I get the new crystal and if I have any luck with the ZX81 rom. Thanks for doing this! David Knab

On Fri, Mar 5, 2021 at 12:38 PM mahjongg2 notifications@github.com wrote:

Nice!

Do you have the latest PCB, if not it needs patches for slow mode!

To be hones, I have still not built my own board, as I’m quite disabled due to lockdown, my asthma has become crippling, and I’m very tired always. I found all the parts, I have the PCB,. and a simple but suitable soldering iron, but Revspace is completely closed, so I can go there. I’m hoping to recover and get my strength back.

I’m wondering why the ZX81 rom doesn’t work, but that it works as a ZX80 is good news, I wasn’t certain of that.

Did you put the same code in the 16K ROM twice?. it needs that to be like an 8K ROM!

There is quite some activity round the ZX81 as many people are celebrating its 40th anniversary. I’m replaying to some posts with a link to my GitHub and revspace posts.

a 13MHz xtal should be necessary, as 12MHz, is quite far off for correct video timing! Farnell should have one!, also loading and saving can be affected, especially if you load original games and such.

keep trying, did you visit the german forum (if you can read German, I can) you can find it here: So sieht meine ZX81-Klonplatine aus < https://forum.tlienhard.com/phpBB3/viewtopic.php?f=2&t=3266> various persons have gotten my ZX-81+38 to work, after these people found a few hardware bugs, I have made the changes.

there is also an english language discussion group discussing the ZX81+38, here: I started on my new ZX-81 replacement board (kit) ZX81+38 < https://www.sinclairzxworld.com/viewtopic.php?p=35160#p35160>

Good luck!

Op 5 mrt. 2021, om 18:05 heeft dkknab notifications@github.com het volgende geschreven:

Got your zx81/80 board going tonight. Used 12mhz crystal though it wouldn't start consistently. Also used ZX80 rom loaded on AT28C256 making the changes per the board. Couldn't get ZX81 rom to work... not sure why though it may be due to the lower crystal. Also couldn't get it to load from WAV files from phone on first try using ZX80 ROM.

— You are receiving this because you commented. Reply to this email directly, view it on GitHub <

https://github.com/mahjongg2/ZX81plus38/issues/1#issuecomment-791553664>, or unsubscribe <

https://github.com/notifications/unsubscribe-auth/ACAHA4ARZNIC3BW43AKIBYLTCEFPPANCNFSM4OLQ5RKQ

.

— You are receiving this because you commented. Reply to this email directly, view it on GitHub < https://github.com/mahjongg2/ZX81plus38/issues/1#issuecomment-791573565>, or unsubscribe < https://github.com/notifications/unsubscribe-auth/ASNSXJD3G3NNDXQGKTL2VCLTCEJJPANCNFSM4OLQ5RKQ

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— You are receiving this because you commented. Reply to this email directly, view it on GitHub < https://github.com/mahjongg2/ZX81plus38/issues/1#issuecomment-791584010>, or unsubscribe < https://github.com/notifications/unsubscribe-auth/ACAHA4FEL4WML3QGLRFLHZ3TCELQBANCNFSM4OLQ5RKQ .

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dkknab commented 3 years ago

PS the pcb board for the keyboard would probably take you no time to design. I wire wrapped mine on the blank pcb you see in the pictures. It works great on a sinclair time 1000 and with you zx81plus38 board too.

On Fri, Mar 5, 2021, 1:21 PM mahjongg2 notifications@github.com wrote:

Dear David,

First I’m located in the Netherlands and yes, the revision 1.6 Board is the latest, and should work fine, according to both the English and german forums, you can translate the german texts using copy/paste, and the google translate site.

I’m a bit shocked that 12MHz generates a good picture, I know that the original 6.5 Mhz resonators are not very precise, but 6 and 6.5 MHz, that is eight percent or so difference, and TV’s are very finicky about timing, even for a black and white signal.

I have been gifted a 1.6 PCB, so I have one, and a few older (1.4) versions too) I could patch up.

did you check the jumping for the AT28C256 (OTP) rom, as there are several jumpers that can be changed for older ROM’s, but AFAIK the default should be good for 32K ROM’s, and yes, I always put multiple copies, at 8K borders in, just so that there is less chance you put the 8K image at the wrong location in ROM, and yes at 8K borders, so 0K 8K 16K and 24K

I’m thinking about designing a specific keyboard PCB for the ZX81+38 too, although the ZX81+34 compatible keyboard works works fine.

Farnell has a website and operates worldwide.

best regards, Martin de Jong (mahjongg)

Op 5 mrt. 2021, om 18:57 heeft dkknab notifications@github.com het volgende geschreven:

Thanks for the response. Let me see if I can share what I've done in response to your questions. I will start by saying I am a complete novice. I started with Ben Eater's 6502 project and have taken off from there making 6502 boards and Z80 boards.

First off I am using the REV 1.6 board...the last one I believe you posted. I got some from PCBway and JLCPCB. I'm not sure at all what you mean by the patches for slow mode as I'm guessing it does not apply to REV1.6

I do have some extra boards - this was the first time I ordered a PCB so I ordered some from PCBWay and JLCPCB. I have 10 boards in all so if you know someone who needs one I can share it with them if that's ok with you.

Sorry to hear you are not 100%. I know for me working on these projects is a distraction. I hope you get well soon!

I was thinking the reason the ZX81 rom doesn’t work is because of the crystal. Once I get a 13mhz crystal I'll try the ZX81 rom again. It's neat with the ZX80. I made the keyboard pictured on github. I didn't realize the ZX80 keyboard is slightly different than the ZX81. I have two of the TIMEX Sinclair 1000s that I've been messing with too.

I am using the AT28C256 eeprom which is 32K I believe. I only put in the ZX81 code once. I'll have to load it a few times. Where do I start the subsequent images of the code on the eeprom? Do I put it at 0K, then 8K, 16K and finally 24K locations?

I was completely surprised too that the 12MHz crystal works for the ZX80. At least I know the board works just fine. I have ordered the 13mhz crystal's from Mouser here in the US -I haven't tried to order from Farnell. Where are they located?

AS I mentioned too I can't load from a audio file so the fact I have the 12mhz crsytal must be impacting that too.

I will keep trying. I do not read or speak German but maybe through the wonder of the internet it will translate it for me. I'll be sure to check it out as well as the english version of the discussion group you mentioned.

I'll let you know how things go especially when I get the new crystal and if I have any luck with the ZX81 rom. Thanks for doing this! David Knab

On Fri, Mar 5, 2021 at 12:38 PM mahjongg2 notifications@github.com wrote:

Nice!

Do you have the latest PCB, if not it needs patches for slow mode!

To be hones, I have still not built my own board, as I’m quite disabled due to lockdown, my asthma has become crippling, and I’m very tired always. I found all the parts, I have the PCB,. and a simple but suitable soldering iron, but Revspace is completely closed, so I can go there. I’m hoping to recover and get my strength back.

I’m wondering why the ZX81 rom doesn’t work, but that it works as a ZX80 is good news, I wasn’t certain of that.

Did you put the same code in the 16K ROM twice?. it needs that to be like an 8K ROM!

There is quite some activity round the ZX81 as many people are celebrating its 40th anniversary. I’m replaying to some posts with a link to my GitHub and revspace posts.

a 13MHz xtal should be necessary, as 12MHz, is quite far off for correct video timing! Farnell should have one!, also loading and saving can be affected, especially if you load original games and such.

keep trying, did you visit the german forum (if you can read German, I can) you can find it here: So sieht meine ZX81-Klonplatine aus < https://forum.tlienhard.com/phpBB3/viewtopic.php?f=2&t=3266> various persons have gotten my ZX-81+38 to work, after these people found a few hardware bugs, I have made the changes.

there is also an english language discussion group discussing the ZX81+38, here: I started on my new ZX-81 replacement board (kit) ZX81+38 < https://www.sinclairzxworld.com/viewtopic.php?p=35160#p35160>

Good luck!

Op 5 mrt. 2021, om 18:05 heeft dkknab notifications@github.com het volgende geschreven:

Got your zx81/80 board going tonight. Used 12mhz crystal though it wouldn't start consistently. Also used ZX80 rom loaded on AT28C256 making the changes per the board. Couldn't get ZX81 rom to work... not sure why though it may be due to the lower crystal. Also couldn't get it to load from WAV files from phone on first try using ZX80 ROM.

— You are receiving this because you commented. Reply to this email directly, view it on GitHub <

https://github.com/mahjongg2/ZX81plus38/issues/1#issuecomment-791553664>, or unsubscribe <

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dkknab commented 3 years ago

One last thing... next up I want to 3d print a case. I'd love to do the zx80 case in white since I have 2 timex 1000 cases in black. I have the creality ender v2 printer... talk about fun. I've made all sorts of things both useful and not with it.

David

On Fri, Mar 5, 2021, 1:21 PM mahjongg2 notifications@github.com wrote:

Dear David,

First I’m located in the Netherlands and yes, the revision 1.6 Board is the latest, and should work fine, according to both the English and german forums, you can translate the german texts using copy/paste, and the google translate site.

I’m a bit shocked that 12MHz generates a good picture, I know that the original 6.5 Mhz resonators are not very precise, but 6 and 6.5 MHz, that is eight percent or so difference, and TV’s are very finicky about timing, even for a black and white signal.

I have been gifted a 1.6 PCB, so I have one, and a few older (1.4) versions too) I could patch up.

did you check the jumping for the AT28C256 (OTP) rom, as there are several jumpers that can be changed for older ROM’s, but AFAIK the default should be good for 32K ROM’s, and yes, I always put multiple copies, at 8K borders in, just so that there is less chance you put the 8K image at the wrong location in ROM, and yes at 8K borders, so 0K 8K 16K and 24K

I’m thinking about designing a specific keyboard PCB for the ZX81+38 too, although the ZX81+34 compatible keyboard works works fine.

Farnell has a website and operates worldwide.

best regards, Martin de Jong (mahjongg)

Op 5 mrt. 2021, om 18:57 heeft dkknab notifications@github.com het volgende geschreven:

Thanks for the response. Let me see if I can share what I've done in response to your questions. I will start by saying I am a complete novice. I started with Ben Eater's 6502 project and have taken off from there making 6502 boards and Z80 boards.

First off I am using the REV 1.6 board...the last one I believe you posted. I got some from PCBway and JLCPCB. I'm not sure at all what you mean by the patches for slow mode as I'm guessing it does not apply to REV1.6

I do have some extra boards - this was the first time I ordered a PCB so I ordered some from PCBWay and JLCPCB. I have 10 boards in all so if you know someone who needs one I can share it with them if that's ok with you.

Sorry to hear you are not 100%. I know for me working on these projects is a distraction. I hope you get well soon!

I was thinking the reason the ZX81 rom doesn’t work is because of the crystal. Once I get a 13mhz crystal I'll try the ZX81 rom again. It's neat with the ZX80. I made the keyboard pictured on github. I didn't realize the ZX80 keyboard is slightly different than the ZX81. I have two of the TIMEX Sinclair 1000s that I've been messing with too.

I am using the AT28C256 eeprom which is 32K I believe. I only put in the ZX81 code once. I'll have to load it a few times. Where do I start the subsequent images of the code on the eeprom? Do I put it at 0K, then 8K, 16K and finally 24K locations?

I was completely surprised too that the 12MHz crystal works for the ZX80. At least I know the board works just fine. I have ordered the 13mhz crystal's from Mouser here in the US -I haven't tried to order from Farnell. Where are they located?

AS I mentioned too I can't load from a audio file so the fact I have the 12mhz crsytal must be impacting that too.

I will keep trying. I do not read or speak German but maybe through the wonder of the internet it will translate it for me. I'll be sure to check it out as well as the english version of the discussion group you mentioned.

I'll let you know how things go especially when I get the new crystal and if I have any luck with the ZX81 rom. Thanks for doing this! David Knab

On Fri, Mar 5, 2021 at 12:38 PM mahjongg2 notifications@github.com wrote:

Nice!

Do you have the latest PCB, if not it needs patches for slow mode!

To be hones, I have still not built my own board, as I’m quite disabled due to lockdown, my asthma has become crippling, and I’m very tired always. I found all the parts, I have the PCB,. and a simple but suitable soldering iron, but Revspace is completely closed, so I can go there. I’m hoping to recover and get my strength back.

I’m wondering why the ZX81 rom doesn’t work, but that it works as a ZX80 is good news, I wasn’t certain of that.

Did you put the same code in the 16K ROM twice?. it needs that to be like an 8K ROM!

There is quite some activity round the ZX81 as many people are celebrating its 40th anniversary. I’m replaying to some posts with a link to my GitHub and revspace posts.

a 13MHz xtal should be necessary, as 12MHz, is quite far off for correct video timing! Farnell should have one!, also loading and saving can be affected, especially if you load original games and such.

keep trying, did you visit the german forum (if you can read German, I can) you can find it here: So sieht meine ZX81-Klonplatine aus < https://forum.tlienhard.com/phpBB3/viewtopic.php?f=2&t=3266> various persons have gotten my ZX-81+38 to work, after these people found a few hardware bugs, I have made the changes.

there is also an english language discussion group discussing the ZX81+38, here: I started on my new ZX-81 replacement board (kit) ZX81+38 < https://www.sinclairzxworld.com/viewtopic.php?p=35160#p35160>

Good luck!

Op 5 mrt. 2021, om 18:05 heeft dkknab notifications@github.com het volgende geschreven:

Got your zx81/80 board going tonight. Used 12mhz crystal though it wouldn't start consistently. Also used ZX80 rom loaded on AT28C256 making the changes per the board. Couldn't get ZX81 rom to work... not sure why though it may be due to the lower crystal. Also couldn't get it to load from WAV files from phone on first try using ZX80 ROM.

— You are receiving this because you commented. Reply to this email directly, view it on GitHub <

https://github.com/mahjongg2/ZX81plus38/issues/1#issuecomment-791553664>, or unsubscribe <

https://github.com/notifications/unsubscribe-auth/ACAHA4ARZNIC3BW43AKIBYLTCEFPPANCNFSM4OLQ5RKQ

.

— You are receiving this because you commented. Reply to this email directly, view it on GitHub < https://github.com/mahjongg2/ZX81plus38/issues/1#issuecomment-791573565>, or unsubscribe < https://github.com/notifications/unsubscribe-auth/ASNSXJD3G3NNDXQGKTL2VCLTCEJJPANCNFSM4OLQ5RKQ

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dkknab commented 3 years ago

Just thought I'd let you know I was able to get the zx81 rom loaded and running. The sound input to load programs also works. Here's a picture of frogger... game over though.

David

On Fri, Mar 5, 2021, 2:13 PM David Knab @.***> wrote:

One last thing... next up I want to 3d print a case. I'd love to do the zx80 case in white since I have 2 timex 1000 cases in black. I have the creality ender v2 printer... talk about fun. I've made all sorts of things both useful and not with it.

David

On Fri, Mar 5, 2021, 1:21 PM mahjongg2 @.***> wrote:

Dear David,

First I’m located in the Netherlands and yes, the revision 1.6 Board is the latest, and should work fine, according to both the English and german forums, you can translate the german texts using copy/paste, and the google translate site.

I’m a bit shocked that 12MHz generates a good picture, I know that the original 6.5 Mhz resonators are not very precise, but 6 and 6.5 MHz, that is eight percent or so difference, and TV’s are very finicky about timing, even for a black and white signal.

I have been gifted a 1.6 PCB, so I have one, and a few older (1.4) versions too) I could patch up.

did you check the jumping for the AT28C256 (OTP) rom, as there are several jumpers that can be changed for older ROM’s, but AFAIK the default should be good for 32K ROM’s, and yes, I always put multiple copies, at 8K borders in, just so that there is less chance you put the 8K image at the wrong location in ROM, and yes at 8K borders, so 0K 8K 16K and 24K

I’m thinking about designing a specific keyboard PCB for the ZX81+38 too, although the ZX81+34 compatible keyboard works works fine.

Farnell has a website and operates worldwide.

best regards, Martin de Jong (mahjongg)

Op 5 mrt. 2021, om 18:57 heeft dkknab @.***> het volgende geschreven:

Thanks for the response. Let me see if I can share what I've done in response to your questions. I will start by saying I am a complete novice. I started with Ben Eater's 6502 project and have taken off from there making 6502 boards and Z80 boards.

First off I am using the REV 1.6 board...the last one I believe you posted. I got some from PCBway and JLCPCB. I'm not sure at all what you mean by the patches for slow mode as I'm guessing it does not apply to REV1.6

I do have some extra boards - this was the first time I ordered a PCB so I ordered some from PCBWay and JLCPCB. I have 10 boards in all so if you know someone who needs one I can share it with them if that's ok with you.

Sorry to hear you are not 100%. I know for me working on these projects is a distraction. I hope you get well soon!

I was thinking the reason the ZX81 rom doesn’t work is because of the crystal. Once I get a 13mhz crystal I'll try the ZX81 rom again. It's neat with the ZX80. I made the keyboard pictured on github. I didn't realize the ZX80 keyboard is slightly different than the ZX81. I have two of the TIMEX Sinclair 1000s that I've been messing with too.

I am using the AT28C256 eeprom which is 32K I believe. I only put in the ZX81 code once. I'll have to load it a few times. Where do I start the subsequent images of the code on the eeprom? Do I put it at 0K, then 8K, 16K and finally 24K locations?

I was completely surprised too that the 12MHz crystal works for the ZX80. At least I know the board works just fine. I have ordered the 13mhz crystal's from Mouser here in the US -I haven't tried to order from Farnell. Where are they located?

AS I mentioned too I can't load from a audio file so the fact I have the 12mhz crsytal must be impacting that too.

I will keep trying. I do not read or speak German but maybe through the wonder of the internet it will translate it for me. I'll be sure to check it out as well as the english version of the discussion group you mentioned.

I'll let you know how things go especially when I get the new crystal and if I have any luck with the ZX81 rom. Thanks for doing this! David Knab

On Fri, Mar 5, 2021 at 12:38 PM mahjongg2 @.***> wrote:

Nice!

Do you have the latest PCB, if not it needs patches for slow mode!

To be hones, I have still not built my own board, as I’m quite disabled due to lockdown, my asthma has become crippling, and I’m very tired always. I found all the parts, I have the PCB,. and a simple but suitable soldering iron, but Revspace is completely closed, so I can go there. I’m hoping to recover and get my strength back.

I’m wondering why the ZX81 rom doesn’t work, but that it works as a ZX80 is good news, I wasn’t certain of that.

Did you put the same code in the 16K ROM twice?. it needs that to be like an 8K ROM!

There is quite some activity round the ZX81 as many people are celebrating its 40th anniversary. I’m replaying to some posts with a link to my GitHub and revspace posts.

a 13MHz xtal should be necessary, as 12MHz, is quite far off for correct video timing! Farnell should have one!, also loading and saving can be affected, especially if you load original games and such.

keep trying, did you visit the german forum (if you can read German, I can) you can find it here: So sieht meine ZX81-Klonplatine aus < https://forum.tlienhard.com/phpBB3/viewtopic.php?f=2&t=3266> various persons have gotten my ZX-81+38 to work, after these people found a few hardware bugs, I have made the changes.

there is also an english language discussion group discussing the ZX81+38, here: I started on my new ZX-81 replacement board (kit) ZX81+38 < https://www.sinclairzxworld.com/viewtopic.php?p=35160#p35160>

Good luck!

Op 5 mrt. 2021, om 18:05 heeft dkknab @.***> het volgende geschreven:

Got your zx81/80 board going tonight. Used 12mhz crystal though it wouldn't start consistently. Also used ZX80 rom loaded on AT28C256 making the changes per the board. Couldn't get ZX81 rom to work... not sure why though it may be due to the lower crystal. Also couldn't get it to load from WAV files from phone on first try using ZX80 ROM.

— You are receiving this because you commented. Reply to this email directly, view it on GitHub <

https://github.com/mahjongg2/ZX81plus38/issues/1#issuecomment-791553664>, or unsubscribe <

https://github.com/notifications/unsubscribe-auth/ACAHA4ARZNIC3BW43AKIBYLTCEFPPANCNFSM4OLQ5RKQ

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mahjongg2 commented 1 year ago

well I finally got my own copy working, I had a revision 1.6 PCB too, and the changes that were needed were: replacing the 74HC14 inverter with a 74HC04 inverter, as a crystal oscillator won't work with schmitt trigger inputs. Replacing all logic IC's with 74HCxx logic, as a mix of 74LS and 74HC will often not work. If your inverse K prompt is is all black then you also need the timing improvement provided by inverting the CPU clock using half of U18 the 74HC74, see revision 1.8 schematics. Also note that the order of pin's for the 5-pin keyboard data is reverted, fixed in revision 1.8. That might be relevant if you want to connect a real ZX-81 keyboard foil. as its almost impossible to twist the keyboard foil, so use a revision 1.8 PCB, BOM schematic, etc.

mahjongg2 commented 1 year ago

Just finished revision 1.9, the only changes from rev 1.8 is that R23 was changed to 1K and I added five pulldown 10K resistors on the bases of the 2N3904 transistors in my joystick interface, which should also work in ZX80 mode.

mahjongg2 commented 1 year ago

I just finished revision 1.10, the only changes are the location of some 2.5mm holes used to mount the PCB in the real zx-81 case.