What do you (or would you) use for ROM replacement on the CPC6128 ? I'd like to avoid "one-time" or old-school-uv-erasable stuff (like 27c256). 28c256(eeprom) are hard/expensive to source. I've got a couple at29c256 (atmel flash), but that doesn't work as is.
There seems to be an ambiguity for the pin 1 on those chips:
* on the official cpc schematics, it's "NC" on the 40025 and connected to +5v on the 40015
* on perlrun PCB, pin1 for 40025 is "GND" and pin1 for 40015 is +5V. That corresponds to the original PCB pictures (i assume that's what the layers User.BCu and User.FCu are)
* on my own 6128, pin1 for 40015 is indeed +5v but, but pin1 for 40025 seems to float. It's definitely not gnd or +5V
The AT29c256 probably wants 5V on pin1/VPP, but even then, the CPC wont start.
You connect pin1 as you like and load the ROM into the upper or lower half of the 2XC256 as you like..
Well, as said, it just doesn't work. I've programmed the whole 32k, with OS_6128.ROM in lower 16k and BASIC_1.1.ROM in upper 16k. The sha1sum of the whole corresponds to what people have posted on the net. The programmer didn't report any error, even after the mandatory re-reading/check.
But my main question was : which chip would you use ? I understand very well it should be a 2xc256, jedec-compatible stuff. But I have a hard time sourcing them in the usual suspects (digikey, mouser, aliexpress, lcsc).
Is resistor R112 working?
What do you see on your screen?
Does the computer with a different ROM work?
r112 looks fine, and measures ~2.2k, which seems as it should.
The CPC works fine with the original ROM, both before, and after testing the at29.
The screen stays black.
I sometimes have a dark-greenish rectangle, but i'm almost sure it's a remnant of previous testing. It doesn't appear after a long off-state.
Are you sure RESET on Z80 pin 26 is high? Try resetting it low on /BUSRESET
Quote from: McArti0 on 19:24, 04 August 25Are you sure RESET on Z80 pin 26 is high? Try resetting it low on /BUSRESET
I've checked and pin26 is high.
I tried connecting /busreset to gnd for a short time, nothing happened.
Try WAIT signal to GND and turn on CPC.
On D0-D7 there should be byte &01 (first in ROM) and on A0-A15 address &0000.
You can also make a simple stepper from two or three diodes like here...
;schem: WAIT-----|>|---- xxx----M1
; WAIT-----|>|---- xxx----IORQ
; WAIT-----|>|---- xxx----WR
; WAIT-----|>|---- xxx----RD
https://youtu.be/9e_AJJ8AfyQ
Quote from: McArti0 on Yesterday at 09:24You can also make a simple stepper from two or three diodes like here...
Amazing !
You got centronics ports ? Or you did change your expansion port ? I have the usual pcb edge one, doesn't seem as easy to connect wires :-/
you can hold the Z80 pins: WAIT-24, M1-27, WR-22, RD-21, IORQ-20