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MEGA65 / mega65-core

MEGA65 FPGA core
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MEGA65 does not boot if an external POWERED OFF Disc Drive is connected to IEC #247

Open adtbm opened 4 years ago

adtbm commented 4 years ago

If an external drive 1581/1541-II is connected to the MEGA65 but is not powered on, the MEGA65 will not boot into C65, it does boot into C64, when MEGA-Key is pressed while switching MEGA65 on.

gardners commented 4 years ago

This will be due to the powered-off drive holding one or more of the IEC lines low, which the C65 DOS misinterprets as there being a device connected. Please try making an IEC cable with pull-up resistors to see if this resolves the problem, while not stopping normal IEC operation. If so, we should add/strengthen the IEC pull-ups on the M65 mainboard.

gardners commented 4 years ago

Confirmed M65 R2 lacks pullups, but C64 has them.

RP6 places 1K pullup to 5V on clock, data and ATN:

http://www.zimmers.net/anonftp/pub/cbm/schematics/computers/c64/250469-rev.B-left-corrected2.gif

C128 also puts pull-ups on the SRQ line via RP5.4:

http://www.zimmers.net/anonftp/pub/cbm/schematics/computers/c128/310378-3-left.gif

We need to make sure that Antti is adding these in the list of missing pullups on the R3 PCB

deftmega commented 3 years ago

The problem is not completely gone with R3. If 1541-II is connected over IEC and turned off, machine will do (tested with DevKit release default disk image): a) Lock-up during autoboot in C65 Basic b) Ignore full speed (40 Mhz) switch c) Randomly lock up in C65 Mode

please see: https://streamable.com/1q5d1v