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  1. K

    Trying to ID EGA card.

    In my experience most EGA clone cards also copied the switch settings from IBM's EGA card, so you should be able to configure it by following the IBM documentation...
  2. K

    NEC V20 "-8" CPU clocked at 10MHz

    I run a V20 -8 chip in my 10mhz turbo XT machine, no issues at all with this particular chip. As with all overclocking your mileage may vary. If you've already got an -8 chip then why not give it a try and see what happens?
  3. K

    8088 ALU Reference Design Details: Where?

    The 8086/88 also uses its ALU to perform the EA (effective address) calculations for memory operands e.g. [BX+SI+disp16] and similar; one of the enhancements NEC made in the V20 to speed it up a bit was providing a dedicated adder for EA generation.
  4. K

    8088 ALU Reference Design Details: Where?

    All that I can think of is Ken's fairly recent look at the die of the 8086 processor, which doesn't go into much detail about the ALU. But his blog has lots of other content and I'm pretty sure he also did an in-depth look at the Z80's ALU a while back.
  5. K

    Safe to open up an mfm hdd to try and fix it?

    I had a very dead MFM drive (the kind of dead that involves screeching noises as the heads crash into the platters) so took it apart just for fun. Do not under any circumstances touch the platters with your fingers. The beautiful shiny surface is a magnet for fingerprints!
  6. K

    Diagnosing sick Turbo XT clone board

    Great news! Yes, sadly just figuring out what went bad (chip, trace, capacitor, etc.) is at least 9/10ths of the entire battle when repairing these things...
  7. K

    Diagnosing sick Turbo XT clone board

    I've successfully used the 5160 schematics to diagnose two different turbo XT clone motherboards, so in my experience they tend to change very little (mainly just various hacks in the vicinity of the 8288 clock generator for the turbo mode). I had a dead 5150 motherboard where the issue was a...
  8. K

    Area 5150 for IBM PC 4.77MHz

    That's a very good video, and it's focused well enough to see some scanlines, which I think really contributes to the 'feels' of this amazing demo! Graphics (and the transitions!) extending into the overscan area is one of the major accomplishments of Area 5150 because, just like most of the...
  9. K

    Area 5150 for IBM PC 4.77MHz

    Not to mention that the MDA dot clock runs off a separate crystal so you can't do cycle-counting either.... so your code would have to spend quite a bit of time polling the status bits to try and keep in sync with the beam....
  10. K

    Diagnosing sick Turbo XT clone board

    A while back my 5150 died and I had to replace one of the address bus drivers because one of the address lines wasn't working. The '245 transceiver is (essentially) two unidirectional bus drivers sharing the same set of pins, so it's not too surprising that it still works in one direction...
  11. K

    How much did cost a genuine IBM VGA card in 1987/88?

    I wonder if anyone (other than perhaps PS/2 owners) ever bought the IBM VGA card? And if so why? IIRC it did not take long at all for the clones to appear, as several good EGA chipsets were already in production at the time and VGA is (mostly) just "EGA with a RAMDAC"...
  12. K

    Area 5150 for IBM PC 4.77MHz

    This demo is a masterpiece that tricks the CGA into doing stuff that everyone knows it can't do! I was able to run it on my 5150 with dual 360K drives (and 640K memory of course) by spreading the files across two floppies, booting with DOS 3.30 and running APPEND B: before putting the demo...
  13. K

    IBM 5150 - No POST

    The BIOS configures channel 1 (DMA refresh, output on pin 13) of the 8253 timer relatively early - the only tests that happen before initializing the timer are the CPU test (flags and registers) and the ROM checksum. If either of those tests fail, the BIOS simply halts the CPU and the system...
  14. K

    Hello to vintage assembly coders

    Was it Help-PC? It's a fairly old (only covers up to the 80386 instructions) hypertext browser TSR that covers BIOS and DOS interrupts, x86 assembly, and other assorted topics.
  15. K

    IBM 5151 making a loud whining noise after warming up

    I have an IBM 5151 display that is working great (stable raster, good brightness, decent focus) except that it starts making an awful whining noise after about 20-30 minutes of use. Turning the display off and letting it rest for an hour doesn't have any effect. Once it's started to make the...
  16. K

    Odd EGA Feature Connector Voltages...

    Ah, gotcha. Looking more closely at the IBM EGA schematics, there are actually two sets of signals on the feature connector: the R/G/B/HIN/VIN inputs, and the R/G/B/H/V OUT 'outputs'. Have you tried connecting the monitor to the 'output' signals? They're meant to let the feature card take...
  17. K

    Turbo XT that suffers filesystem corruption when in 'turbo' mode (only)

    Also, I haven't been able to find much at all about this machine online. Perhaps some photos will help someone to recognize it? The motherboard says "LOGI PC88XT" (obscured by the ISA cards). Unfortunately the hard drive in the machine refuses to spin up when power is applied, i.e...
  18. K

    Turbo XT that suffers filesystem corruption when in 'turbo' mode (only)

    So this is a real head-scratcher... I recently acquired a Logicraft 88-XT machine, which is a generic Turbo XT system with 640K of RAM and an NEC V20 processor (in a socket labelled "8088-2") that runs at either 4.77Mhz or 8Mhz. I can't find schematics or a manual for this machine, but the...