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mahjongg2 / ZX81plus38

Mij latest ZX81 clone without ULA built from discrete pin through hole components
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RP1 #3

Open ulysses66 opened 3 years ago

ulysses66 commented 3 years ago

RP1 on the schematics Rev1.4BW and BOM don't match. Schematics show 4k7 and BOM shows 10k

mahjongg2 commented 3 years ago

Okay, it really doesn’t make much difference, as they are just pull ups, but in this case they correct value is 10K, because in the ZX81+35 used 10K resistors.

I will correct the schematic, and will re-upload the schematic.

Thanks for the tip

Op 27 sep. 2020, om 16:15 heeft ulysses66 notifications@github.com het volgende geschreven:

RP! on the schematics Rev1.4BW and BOM don't match. Schematics show 4k7 and BOM shows 10k

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mahjongg2 commented 3 years ago

P.S. the lowering of these resistors to 4K7 may have had something to do with the error in the wires to the keyboard, specifically the fact that erroneously the "A8" keyboard line was connected not to A8, but to A8', which is fixed in revision 1,6

mahjongg2 commented 3 years ago

This is still an important change, with 4K7 pullups there were reports that pressing two keys simultaneously the ZX-81+38 could crash. So use 10K pullups!

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. 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. Here's some pictures to show my progress. 20210304_210103

dkknab commented 3 years ago

20210304_210123

mahjongg2 commented 1 year ago

if the 13MHz crystal doesn't work properly you might have used a 74HC14, that is incorrect as a 74HC14 uses schmitt trigger inputs that cannot be driven (well) with a crystal, so please replace the IC with a 74HC04, or better yet with a 74HCU04, and use the correct crystal the 13.000MHz one, or all (Video) timings will deviate.

Have fun with your ZX81+38.