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Thread: Memory Compatibility Z80 vs 8080

  1. #1

    Default Memory Compatibility Z80 vs 8080

    I read in a manual for a S-100 Vector Graphics memory card that it was for use with a Z80 and wouldn't work with the 8080. But they did not explain why. Since the card was designed for the S-100 bus (and should work with standard bus signals ?) what would it be about it that would stop it from working in an 8080 computer ?

  2. #2

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    ...with regard to the above post & question the document is here page 1-1 para 1.1 (or page 13 of the pdf):

    http://www.s100computers.com/Hardwar...64K%20DRAM.pdf

  3. #3
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    I expect it is relying on the Z80 to run the DRAM refresh cycles. That is hinted at in the restriction of the longest DMA burst latency in the specifications section.

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    Note section 2.1.1. The RFRSH signal needs to be on pin 66 of the S100 bus. Pin 66 on the standard S100 bus isn't defined--and the 8080 doesn't produce a RFRSH signal, nor does it have a refresh counter or register. Could a refresh circuit be designed for an 8080? Sure. But 8080/8085 usually employ something like an 8202 DRAM Controller, which makes the whole affair much simpler.

  5. #5

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    Quote Originally Posted by Chuck(G) View Post
    Note section 2.1.1. The RFRSH signal needs to be on pin 66 of the S100 bus. Pin 66 on the standard S100 bus isn't defined--and the 8080 doesn't produce a RFRSH signal, nor does it have a refresh counter or register. Could a refresh circuit be designed for an 8080? Sure. But 8080/8085 usually employ something like an 8202 DRAM Controller, which makes the whole affair much simpler.
    Thanks, so its a hardware issue.

    I have tried a Seatle Computer Products (SCP) 16k Ram card in the Sol-20 and it works fine. But I'm wanting a higher capacity single card and looking around at options. Obviously the PT 48k ram would work, but I can't get my hands on one. So I have been looking at other brands of 64k cards.

    I wonder if the SCP 64k Ram board would work in the Sol ? since they made their 16k card compatible.

    Recently I tried the YANG 32k card in the SOL, didn't work, but it could have hardware fault.

    It there a known list of 48k to 64k cards that are known to be compatible with the Sol-20 ?

  6. #6

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    I like the 64K static RAM boards which use the 2K x 8 static RAM chips. These are low power and very reliable. Most can disable 2K blocks to make memory space holes as required for the Sol-20 and North Star FDC. Be careful though, some can only disable a single 2K block or a full 16K block. With most, you can also throw a 2716 or 2732 (half used) EPROM into one of the RAM sockets. I’ve had the best luck with the CompuPro RAM17 as it is easy to disable multiple 2K blocks and is compatible with front panel machines like the Altair.

    For a DRAM board, the Central Data Corp 64K Board is uniquely configurable for a 64K board. It seems to be designed with early systems in mind that need various holes in RAM for PROM, video, FDC, etc.

    Mike

  7. #7

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    Quote Originally Posted by deramp5113 View Post
    I’ve had the best luck with the CompuPro RAM17 as it is easy to disable multiple 2K blocks and is compatible with front panel machines like the Altair.

    Mike
    Interesting, these boards carry the same HM6116P IC's as the Yang board I have been trying to get to work (but the Yang simply has half the number as its 32k) The photo of the Yang board is on this thread:

    http://www.vcfed.org/forum/showthrea...amp-32k-Memory

    They also mention that 2k blocks can be easily disabled and 2716 Eproms can be used. Maybe the Yang board has a fault or needs the refresh signal of the Z80 system, I will investigate.

    Can I deduce from what has been said by Chuck(G) in post #4 that if I come across a memory board that makes no connection to pin 66, that likely it will be 8080/Sol-20 compatible ?

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    Somewhere I have an old SD Systems 64K DRAM board that runs with an 8080 CPU, so DRAM boards for 8080/8085 CPUs do exist.

    I don't know if anyone ever made an S100 SRAM board using the InMOS 16K SRAMs. Those were really fast (and probably expensive).
    Last edited by Chuck(G); August 7th, 2019 at 09:29 PM.

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    Quote Originally Posted by Hugo Holden View Post
    Can I deduce from what has been said by Chuck(G) in post #4 that if I come across a memory board that makes no connection to pin 66, that likely it will be 8080/Sol-20 compatible ?
    Almost certainly,yes--unless there's a weird one out there that uses the RFSH signal on a different S100 pin.

  10. #10

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    Quote Originally Posted by Chuck(G) View Post
    Almost certainly,yes--unless there's a weird one out there that uses the RFSH signal on a different S100 pin.
    Thanks.

    I just checked on the Yang board, pin 66 not used. Si I think one of the IC's has failed probably in the address decoder as it has an LED that is supposed to light hen the board is active.

    It has a lot of DIP switches as it can be set for extended addressing. It looks like address lines A 14 & A15 are used to select the A and B memory IC banks and later combined with A12 and A13 to create the Chip select signals, with A0 to A11 being the address lines for the 6116 IC's.

    A16 thru A21 appear to be used for an optional extended address scheme.

    If I set the A bank to start at say 4000H, I need to send an out instruction to see if I can activate the address decoder for a test...any suggestions ?

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