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Any interest in a PCjr CPU upgrade board?

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  • MicroCoreLabs
    replied
    https://microcorelabs.wordpress.com/...jr-on-the-way/

    It's on the way...

    Leave a comment:


  • ibmapc
    replied
    Originally posted by VERAULT View Post
    Care to share what your silly 5155 mods are and do Greg?
    I'd be glad to. But, I'll start a new thread later today for it so as not to hi-jack this one.

    Leave a comment:


  • maxtherabbit
    replied
    Originally posted by brain View Post
    You can buy those headers from Digikey/Mouser. I sell a machine pin version in my store:

    http://store.go4retro.com/ic-header/

    The pins on these are very narrow, and do not affect cheap wiper sockets. But, you can also buy the flat pin versions (they cost more):

    https://www.digikey.com/products/en/...=1&pageSize=25

    Aries sells them (looks like they only have forked pin option at Digikey, but they sell the simple post version as well. I used to buy them, and they work fine.
    On your site you specify the pin diameter is 0.060" - is that a mistake? That's larger than a standard PTH for a .100" pin header

    Leave a comment:


  • VERAULT
    replied
    Originally posted by ibmapc View Post
    Yep. Kind of silly. But silly mods make these old machines a blast to play with. I have three 5155s. Only one is stock. Other two have a bunch of "Really Silly MODS". I play with all three but the modded ones tend to get used more.

    Greg
    Care to share what your silly 5155 mods are and do Greg?

    Leave a comment:


  • ibmapc
    replied
    Originally posted by mbbrutman View Post
    Hi Ted,

    ... A super fast PCjr is kind of silly. ;-0
    Yep. Kind of silly. But silly mods make these old machines a blast to play with. I have three 5155s. Only one is stock. Other two have a bunch of "Really Silly MODS". I play with all three but the modded ones tend to get used more.

    Greg

    Leave a comment:


  • ajacocks
    replied
    I’d definitely be interested.

    - Alex

    Leave a comment:


  • mbbrutman
    replied
    Hi Ted,

    I'm a big fan of your work. The price is right for such a unique design and I'd take one. But it's basically for giggles ... I have 486 and Pentium machines around. A super fast PCjr is kind of silly. ;-0

    Leave a comment:


  • Simplethings
    replied
    Yeah I'm late to the game but I'd buy this if would work with my PS/2 model 25.

    Leave a comment:


  • VERAULT
    replied
    Sorry for jumping in late. Im interested. I have 4 pcjrs

    Leave a comment:


  • MicroCoreLabs
    replied
    Nice headers... I think one of those should work!

    Just brainstorming, but since a 512KB SRAM would be attached to the FPGA and available to the CPU, in theory a portion of it could be optionally remapped to cover, among other things, the extension BIOS address range so the Universal XTIDE BIOS could be used.

    After the initial PCjr boot the address range would be populated by software on diskette. It would then jump to the cold-reset vector so the new ROM(s) would be detected by the PCjr's BIOS.

    If there was a CF header on the board it would allow hard drive functionality similar to jr-IDE...

    Leave a comment:


  • brain
    replied
    You can buy those headers from Digikey/Mouser. I sell a machine pin version in my store:

    http://store.go4retro.com/ic-header/

    The pins on these are very narrow, and do not affect cheap wiper sockets. But, you can also buy the flat pin versions (they cost more):

    https://www.digikey.com/products/en/...=1&pageSize=25

    Aries sells them (looks like they only have forked pin option at Digikey, but they sell the simple post version as well. I used to buy them, and they work fine.

    Leave a comment:


  • Eudimorphodon
    replied
    Maybe the photo isn't clear enough to be sure, but it looks like that's made out of machine pins. Plugging something like that into the standard cheap wiper sockets tends to kind of mess them up if you ever want to put the original CPU back in.

    Leave a comment:


  • MicroCoreLabs
    replied
    https://www.ebay.com/itm/IBM-PCjr-HO...UAAOSw5PhfFfvo


    This 40-pin "underside" socket looks interesting. I wonder if it is off-the-shelf or something they custom made.

    Leave a comment:


  • Eudimorphodon
    replied
    Originally posted by eeguru View Post
    The PCjr is a minimum mode implementation of the 8088. But I don't see any reason why it wouldn't work in a maximum mode system or with an extra bus buffer - a 8086 socket/mode with some BIO changes. However the PCjr (and Tandy 1000) is somewhat unique in that they both do not have a DMA controller.
    Since "Tandy 1000" came up I'll throw in that an accelerator like this would have a lot of potential for the original 8088 Tandy 1000s, especially the oddball EX/HX models for which no other practical options currently exist. In those machines you would be dealing with some pretty severe space constraints, both horizontally and vertically, so a miniaturized DIP-size package would have a lot of advantages as long as it could be made short enough to clear an installed PLUS card sitting overhead.

    (Of course one of the complications with a Tandy 1000 is it *may* have a DMA controller; an original conventionally slotted one almost certainly will because 128k didn't go that far even when they were new. You could of course pull it out in all the 8088 T1000s except the SX if you had RAM on the accelerator, though in an EX or HX you might need to sub a different DMA-less board to continue supplying a Plus-slot breakout for additional expansion.)

    Just spitballing, here's another idea for Tandy 1000s, if there's someone who has the assembly-language chops: normally in the 8088 machines you can only add expansion memory up to 640k minus however much RAM is onboard and connected to the video controller. (Either 128k or 256k) This means that these machines always lose at least 16k of DOS memory to video requirements, and it also means in the 7.16mhz machines a chunk of memory is a lot slower than the expansion RAM. (If some benchmarking I've done is correct the RAM built into an 1000EX or HX effectively only runs at 4.77mhz.) The memory tests loop in these machines only counts up to 384k/512k of expansion memory and will insist on this sharing behavior even if you were to stick a full 640k in. However the 80286-powered Tandy 1000 TX's motherboard, which with its normal complement of 512k "fast ram" and 128k video RAM behaves the same way, also allowed sticking in an addition 128k of fast RAM, and if it detects it on power-up the BIOS programs the video chip so the memory behind it no longer appears in the base 640k window and is only paged around the B0000-BFFFF area. I know from some crude experimentation that at least the EX and HX (and presumably the SX, since they all use the same chipset) appear to support in hardware programming the video hardware the same way. (It's in the technical manuals as well; the details are a little piecemeal but if you combine the info from about three different sources it's all there.) I don't know if you can do the same trick with the original 1000s with discrete video, however. Don't have one to fool with.

    Anyway, what would be a neat trick is if a smart person could analyze the differences between the RAM test and video setup/mode switching areas of the EX/HX/SX BIOSes and the TX BIOS and produce a patched 8088 BIOS that would recognize a 640k base RAM upgrade and configure the video chipset accordingly. For an accelerator like that described it'd be a significant boon since you'd be free to ignore all the complications that otherwise arise if you try to "overlay" fast memory on top of the built-in RAM that's pulling double-duty as VRAM and system RAM. VRAM would just be VRAM, like a regular video card.

    An HX or EX with an accelerator that can speed it up to the 286-like speeds that it can apparently achieve in a PCjr would be a really desirable machine for playing Tandy 1000-specific games. (As it stands the 8088-powered machines tend to be a little on the slow side.)

    Leave a comment:


  • MicroCoreLabs
    replied
    Regarding the next186... There are a number of x86 cores which will run as fast as the FPGA technology allows... >160Mhz in next186's case? But in my opinion it is more interesting and challenging to have the core be cycle accurate and then run it in the original vintage hardware like the IBM and compatible computers. Only then can you be sure the core is actually correct in both the implementations of the instruction set and the structural features like prefetch queues, interrupt priority ordering, prefixes, arbitration, etc... It is unlikely that the rtl cores can replace the actual 8088 as the MCL86 can...

    I am curious if the next186 can run the test code I uploaded to GitHub... I developed and ran these tests to exercise every opcode and addressing mode of the MCL86 core... It runs successfully on both the real x86 and the MCL86...

    In fact... one thing I ran into when porting it to the PCjr was the fact that I *needed* to run cycle accurate during POST... When I ran it "unlocked" I got a beep and no splash screen. What I needed to do was run it cycle accurate until after the POST, then as soon as an NMI occurred (a PCjr key was pressed) I would then disable the cycle accuracy!

    Anyway.. just a note that cycle accuracy is needed at times and that the "rtl" FPGA cores generally won't work... Even 8088 MPH also won't begin if it senses the CPU is not cycle accurate!

    Leave a comment:

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