Hi Roland,
So we can compare notes about 2MHz and 4MHz operation, could you list the part numbers and speeds of your:
- 6502
- 6522
- 8255
- RAM
- ROM
- '133
Here are mine:
- 6502 - Signetics SY6502 (8219 date code)
- 6522 - Rockwell R6522-31 (9251 date code)
- 8255 - Mitsubishi M5L8255AP-5 (822300 date code)
- RAM - Alliance AS6C1008-55
- ROM - SST 39SF010A
- '133 - 74ALS133
I also have handy some different 6502's:
- Rockwell R65C02P2 (date code 8482)
- Rockwell R65C02P4 (date code 1145, probably fake)
- UMC UM6502CE (date code 1124)
And one different 8255:
- NEC D71055C
(Only with this NEC 8255 will my new Atom run at 4Mhz reliably)
These are my current results with M5L8255AP-5:
- SY6502 - works at 1MHz, 2MHz, hangs at 4MHz
- UM6502CE - works at 1MHz, 2MHz, hangs at 4MHz
- Rockwell R65C02P2 - works at 1MHz, 2MHz, hangs at 4MHz with a small squeak
- Rockwell R65C02P4 - works at 1MHz, 2MHz, keyboard reads random characters at 4MHz
These are my current results with the NEC D71055C:
- SY6502 - works at 1MHz, 2MHz, hangs at 4MHz
- UM6502CE - works at 1MHz, 2MHz, hangs at 4MHz
- Rockwell R65C02P2 - works at 1MHz, 2MHz, hangs at 4MHz
- Rockwell R65C02P4 - works at 1MHz, 2MHz, 4Mhz
Occasionally when changing to 2MHz I'll get a crash. This is hard to reproduce from a BASIC program.
Dave