Started by gerald, 20:31, 17 October 12
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Quote from: gerald on 20:31, 17 October 12I cannot test with a DKTronic extension as I do not own any.
Quote from: arnoldemu on 20:52, 17 October 12EDIT: Gerald which country are you in? I am happy to lend you mine if you are in UK or Europe.
Quote from: gerald on 20:31, 17 October 12So my question is : how the write to DRAM is inhibited when an extension RAM is selected ?
Quote from: IanS on 21:41, 17 October 12I really didn't want to spend time tracing the PCB.Do you want to know about the other transistor on a dktronics ram board?It looks like it's pulling MREQ up to +5v.
Quote from: gerald on 21:50, 17 October 12All these hacks on DKtronic ram extension let me think that the 464 (664?) was not really designed to have a RAM extension.
Quote from: Bryce on 22:47, 17 October 12I still use my 464 and have 512K (2x 256K) DKTronics RAM expansions connected. But I'm starting to wonder if I should remove them. Pulling a negative output that has no inline resistor is a really bad idea and definitely not something I would recommend. I haven't checked the internal circuitry of the Z80, maybe the outputs have some sort of protection. But even then, that would have been designed for "emergencies" and not for regular use.Bryce.
Quote from: gerald on 23:21, 17 October 12@Bryce, Ians, Kevin : can one of you post a picture of the extension both side (scanned ?). Wiki picture are really too small for any analysis.
Quote from: Bryce on 23:57, 17 October 12The 664 service manual is here: Service Manuals - CPCWiki
Quote from: Bryce on 23:57, 17 October 12Would you need to do exactly the same on the 464+? Surely they fixed it there, but I haven't looked (and I don't think any specific 464+ RAM expansions were ever released).
Quote from: IanS on 23:54, 17 October 12I've put a few quick pics here - http://www.testbox2.co.uk/dktronic64K.zip (~6MB)Difficult to get good pics with the edge connectors on each side. And much of the interesting bits happens close to the connector.
Quote from: gerald on 00:33, 18 October 12 The 664 file is cursed (464KB ), and 7zip cannot open it (corrupted ?) I do not think. The DRAM protection is done by the PAL and the PAL is part of the ASIC, and ASIC is the same on all CPC+.I do not have a 464+ to check, but reading 2nd bank should return garbage (floating bus) while on 464 you get 1st bank data. Thanks. As you said, the edge connector is a pain !!Let see what I can get from this.
Quote from: gerald on 23:52, 17 October 12Dodgy hack, not exactly "Best Practise", agreed !But allowing to have more RAM on the expansion port while not planned on original design is a clever trick.I am just wondering the chronology of these expansions. Did they appear before or after the 6128 ?The RAMDIS signal seem to indicate that AMSTRAD planned the ram extension, but just forgot to protect the internal DRAM ?Why no fix has been done on later version of 464 ?By the way, has anyone a 664 service manual ?
Quote from: gerald on 21:27, 18 October 12Next step is to deal with C3 mode. I hope to have a full 6128 compatible behaviour by preventing the ROM to appear at 0x4000-0x7FFF range when enabled.
with ROM disabled :r/w in 0x4000-0x7FFF goes to base bank 0xC000-0xFFFFr/w in 0xC000-0xFFFF goes to extension bank 0xC000-0xFFFF with ROM enabled :w in 0x4000-0x7FFF goes to base bank 0xC000-0xFFFFw in 0xC000-0xFFFF goes to extension bank 0xC000-0xFFFFr in 0x4000-0x7FFF and 0xC000-0xFFFF return upper rom content
Memory Expansion testC0 80 C01C E7 80 80E7 0C E6 E6 E5 E5 E4 E414 00 1C 04
Quote from: gerald on 22:43, 18 October 12Latest news : DKTronics C3 compatible mode is working.
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