Amstrad GX4000 / Plus cartridge PCB

Started by Chinnery, 12:02, 27 May 19

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TotO

#25
Hi Shining,

Please, can you show it working?
I have tested and it doesn't work for me.

Thank you.
"You make one mistake in your life and the internet will never let you live it down" (Keith Goodyer)

Bryce

I use one of these all the time. It has always worked fine with any machine I tried it on.

Bryce.

schombi

My skills in soldering a fairly poor and I have no background in electronics, but I successfully managed to build me a working Batman the Movie cartridge. Thanks for sharing this project!

What I´m still struggling with: I was always under the impression that the ACID chip was always required to use a cartridge on the GX4000 and those chips are hard to get these days. How come this project lets you decide whether to run with or without the ACID chip?

Bryce

Quote from: schombi on 07:53, 09 January 22
My skills in soldering a fairly poor and I have no background in electronics, but I successfully managed to build me a working Batman the Movie cartridge. Thanks for sharing this project!

What I´m still struggling with: I was always under the impression that the ACID chip was always required to use a cartridge on the GX4000 and those chips are hard to get these days. How come this project lets you decide whether to run with or without the ACID chip?

The 74HC112 is setting the appropriate signals at exactly the right time, so the CPC thinks there's a valid ACID chip on the board.

Bryce.

schombi

#29
Many thanks! Has this been only discovered "recently"? Seems like a pretty simple solution. I always thought a more complex workaround (e.g. a CPLD) was required.

pelrun

#30
There's a flaw in the ACID design that's being exploited - the CPC signals that the input from the 'ACID' is wrong long enough before forcing a reset that you can flip the input you're supplying (via the '112) to make it happy again.
https://www.cpcwiki.eu/forum/amstrad-cpc-hardware/acid-chip-inside/msg22291/#msg22291


bobmoo79

#32
Quote from: Shining on 10:55, 05 January 22
Quote from: TotO on 17:58, 03 December 21I have tested this schematic by curiosity, and it looks to not work at all. ;D

May be I have done something wrong...
I don't understand what does special your RC combination compared to the original schematic.


Perhaps my schematic was not clear, cause I missed to describe the signal on the RC-combination:


On the original oscillogram for acid reset (https://www.cpcwiki.eu/index.php/File:ACID_Init_by_Grim.png) you will notice that after startup the sin signal has to be high. Using the original schematic from nilquader, the sin signal after reset is 50% low or high cause it does not follow the reset at all. Now instead of pulling the RC to VCC, I used the CCLR signal not only for CLK+ but also for PRE at the flip flop to force the flipflop to "1" after reset. Also I lowered the time constant for the RC-combination.


I know quite some plusses where this always works and noone reported a single problem until now.


So for clarity, the RC combination is not being pulled to VCC but instead is tied to CCLR? Sorry for being dumb.
I built one of these with the R1 connected to VCC AND CCLR. Didn't work obviously and I presume it's because the RC combo is not able to do its thing (as it's pulled high always.

Cheers.

bobmoo79

#33
So is this the correct interpretation of what 'Shining' posted?
I've connect the top of the R1 to CCLR and CLK (R1 is no longer connected to VCC). I've changed C2 to 100pF.

Initially I tried a 74HC112 flipflop but read somewhere that it should be a 74AC112 as the other is too slow, which seems to contradict the success others show in their posts. Regardless I am now using a  74AC112N and it's still not working.


I spent time last night double checking my PCB against this schematic and it's correct as far as I can tell. I then started modifying it to see if I could try different interpretations of the info presented in this thread but I just can't get it to work no matter what I do.You cannot view this attachment.


Of course I have no real proof that the EPROM is flashed correctly, but I do know that 'EGecu Pro' verifies the EPROM against the ROM and shows it is correct.  Is there any trick to flashing the EPROM? I downloaded a bunch of BIN format ROMS from CPCMania and burned them (I've tried several). I also tried CPR format files (which I converted to BIN using CPRTools) but all I get is a black screen on the TV.

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