Author Topic: DDI4 ram failure  (Read 236 times)

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Offline Elder0010

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DDI4 ram failure
« on: 23:48, 30 August 21 »
Hi, this is my first post here and I am new to the CPC so bear with me :)
I am using the zaxon's DDI4 with my 464, and some software is crashing. I have no issues when playing games not requiring the expansion, but the batman forever demo crashes and pinball dreams (randomly) crashes when you lose a ball.

I ran two diagnostics to test the upper memory:
the m4Duke one
https://github.com/M4Duke/z80/blob/master/RAM512KB.s

and the one from llopis
https://github.com/llopis/amstrad-diagnostics

The first one reports no error, but the one from llopis is crashing while testing the upper ram area. I recorded a video to show the issue:

https://www.youtube.com/watch?v=0wJlvRdx0_M (sorry for the crt flickering).

Basically the program starts to "glitch" when testing Bank 08 of the upper ram. To be 100% sure, I tried to run it also from an EPROM.
Since the lower ram test is passed, I am wondering if the problem is in the computer instead of the expansion. I understand that if there are errors in the ram the program should report it, but it seems like that something in the execution of it is going wrong.
I also tried the quick and dirty ram test (https://www.cpcwiki.eu/forum/amstrad-cpc-hardware/quick-and-dirty-ram-test-for-cpc/) for the lower RAM and it's showing no errors.

Unfortunately I don't have another CPC to test the DDI4.
I didn't check the source code for the diagnostics, but looking at the 464  schematics (https://www.cpcwiki.eu/imgs/6/6d/Schaltplan_cpc_464.jpg) I was thinking that IC109 / IC104 / IC113 and IC105 could cause an addressing issue not detected by the lower RAM tests.

Also, I see that IC116 is responsible for the CAS/RAS signals, perhaps it's related also to the upper RAM bankswitching? I *guess* that there is some bankswitching hardware in the DDI4, since the address bus is  the usual16 bit (A0/A15), but I don't understand which IC in the 464 is responsible for this.
I read this thread about the DDI4 but i can confirm that the capacitors are ok on my board :) At the moment I'm stuck with this and I don't really know if I should do some more investigation on the computer or return the DDI4 :(
« Last Edit: 23:58, 30 August 21 by Elder0010 »
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Offline Shaun M. Neary

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Re: DDI4 ram failure
« Reply #1 on: 23:56, 30 August 21 »
Looks like a thread for @Piotr 😊
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Offline GUNHED

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Re: DDI4 ram failure
« Reply #2 on: 02:17, 31 August 21 »
Welcome to the forum, there were threads about that problem. Just don't find em now.
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Offline JupiterJones

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Re: DDI4 ram failure
« Reply #3 on: 19:22, 31 August 21 »
Hi Elder0010,


Deleted, it does not apply. Next time I swear I'll read more carefully... My bad :picard:
« Last Edit: 19:29, 31 August 21 by JupiterJones »
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