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Recent content by sergey

  1. sergey

    Switching between two 8088 CPUs

    The DMA controller on the PC and XT doesn't use RQ/GT protocol... Instead, when there's a DMA request, the wait logic generates wait states, isolates the CPU from the bus, and lets the DMA do its business. Some clones, particularly chipset based ones, such as FE2010A, PT8010AF, 82C100 do use...
  2. sergey

    Ericsson PC - Keyboard Interface

    ExPLIT got a bit of a puzzle for me... His colleague has an Ericsson PC, and they tried to run my 8088 BIOS on it. Everything seems to work fine, except of the keyboard. I partially disassembled the INT 9/IRQ1 interrupt handler, and apart from typical PC/XT interaction with the 8255 PPI I/O...
  3. sergey

    Some questions about the Xi 8088….

    Regarding the interrupt controller type: It appears that some CMOS PICs (82C59 vs. NMOS 8259) generate spurious interrupts when interrupt inputs are floating / not connected anywhere. This doesn't seem to be a problem with some other CMOS PICs... The fix is pretty simple: solder pull-down...
  4. sergey

    Some questions about the Xi 8088….

    I fixed the issue with the long delay when the PS/2 mouse is not connected a month ago. Please download the latest BIOS. See commit 8fd8cea
  5. sergey

    Book 8088 discovery and modification thread

    8087 co-processor will get hot. But probably not as hot to melt the case ;) There is not that much clearance in the case to install any kind of heatsink... the best I can think of is replacing the plastic door that accesses the CPU/FPU/BIOS with a piece of aluminum, so it will conduct the heat...
  6. sergey

    Book 8088 discovery and modification thread

    Well, I make the Monster FDC. Probably an overkill for what you need it for... If you can solder, you can get the PCB only, and solder a single FDC. If you can't solder... maybe I can do that for you. If you're interested, I can check what would be the price for the components/work.
  7. sergey

    Unidentified Turbo XT Clone has F/C stuck low

    So it appears that you have confirmed that your board uses the naive turbo switching method using F/C signal, so it suffers from all the issues I've described above. Regarding (4) wait states - it is hardware feature, but if the wait state generator is programmable, it would depend on the BIOS...
  8. sergey

    Unidentified Turbo XT Clone has F/C stuck low

    Technically it is not the 4.77 MHz clock what peripherals care about. Here is a bit of info about the 8284 and the clock generation in IBM PC, XT, and their clones: The 8284 supports two clock sources, a built-in oscillator, IBM PC and compatibles typically have a 14.31818 MHz quartz crystal...
  9. sergey

    Book 8088 discovery and modification thread

    Yeah, that sounds like a complicated solution ;) Technically, it might be easier to initialize XUB, read the configuration, set floppy/USB floppy emulation configuration, reset interrupt vectors, and then re-initialize XUB again ;)
  10. sergey

    Book 8088 discovery and modification thread

    That would work assuming you have a CF card. Perhaps might be a Book 8088 specific hack... Another potential issue that XUB (XT-IDE Universal BIOS) get initialized a bit later and it assumes (or might assume) that floppy disks configuration, e.g. number of drives, doesn't change after XUB...
  11. sergey

    Book 8088 discovery and modification thread

    It should be not that difficult to check for the FDC presence... probably something like sending a command to FDC, e.g., sense drive status, and checking the result. As far as the boot selection, ideally Book8088 would have a flash ROM or some kind of configuration storage, so that it would be...
  12. sergey

    Help me to revive this dead ISA floppy disk and serial controller card

    A few questions and comments: Did you test your FDC in another system? Or you are assuming it is good since you don't see any new burned traces? When you reprogram your AT29C010A BIOS ROM, does it verify successfully in the programmer? (And then it fails to verify once you put it in Micro 8088...
  13. sergey

    Book 8088 discovery and modification thread

    Potentially... But will require some mods. At least for the V1, the chip select was generated specifically for OPL2 (388h). Sound blaster or compatible will need also other chip selects... So it will need some bodge wires to address lines.
  14. sergey

    Book 8088 discovery and modification thread

    Most newer LSI ICs are CMOS, that includes RTL8019AS Ethernet controller, various VGA controllers, etc. And they will have CMOS level outputs - very close to VCC == 5V for logic "1", that would work just fine with 74HC. The problem will likely happen when TTL or NMOS outputs are connected to...
  15. sergey

    Book 8088 discovery and modification thread

    Oh, forgot to reply to that... That's a good question, and if we'll get V2 schematic, I bet we'll have an answer. The big chip is the CPLD, and I'd think this is an extension header. Perhaps a trimmed version of ISA bus to connect yet another extension board?
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