Nov 232013
 

Its a very rare occasion that I cannot dump a 16L8 device. There has only ever been once in the past where I have failed in this and that was with a Namco chip that uses heavy feedback.
Recently I’ve been trying to dump the HAL16L8 device from an Amstrad 6128 but its just not happening.

The chip seems to have some kind of flip flop implementation that I cannot reliable dump automatically or figure it out in my head.
I’ve tried quite a few different approaches but cannot get this to work. Even with a logic analyser setup its quite elusive.

I’ve been through all the info I can find online and while it all makes sense, it does not help me implement the equations properly.
The devices I’ve tested are locked so cannot be read out with a programmer but if you have anything to offer or can even supply a proper dump then could you please pass it on.

Thank you

 Posted by at 8:48 pm

  2 Responses to “PAL dumping failure”

  1. judging from the schematics
    http://www.cpcwiki.eu/imgs/4/4a/CPC6128_Schematic.png
    you can see that the 64k memory version doesn’t need the pal chip and it needs only 3 jumper wires.
    from 64k to 128k it should be straightforward to reverse the pal chip…
    or does the cpc6128 use an obscure memory map ?
    also MESS driver could help
    http://mamedev.org/source/src/mess/drivers/amstrad.c.html

    • Hi Zab. The idea behind the the PAL is simple enough, its the actual implementation of it that is strange. You can see from the schematics that the PAL has 3 seemingly unconnected pins at 13, 14 and 15. What these pins do is change state depending on what region of the extended memory is selected and they latch to that state. Again simple enough in theory but this is 16L8 device and not one capable of registered pins so up until recently (thanks again Charles) I didnt know this kind of thing could be implemented into this device.

      I’ve got a test equation written for latching that seems to work so the next job is the write it for the actual switching on the 6128.