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Original-IBM-5150 or IBM-Clone Memory Experimentation Thread

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  • T-Squared
    replied
    Well, looking at the motherboard, it at least suggests that Pin #1 of the 4164s are connected to something, because each one has a trace coming off of them, which is NC on the pinout, so I'm guessing there's more to this.

    Leave a comment:


  • Eudimorphodon
    replied
    Originally posted by T-Squared View Post
    What I'm hoping is that 64kb memory is pin- and interface-compatible, so I simply have to plug the chips in without modification (even then, I wouldn't know what to modify).
    As discussed in the other thread, just changing the 64k chips for 256k ones isn't going to magically result in the machine seeing more memory. The short version is this. Here's the pinouts of the three most common 16 pin DRAM chips you'll find in an a PC/XT. We're concerned with the two rightmost ones:



    See how pin one is "NC" on the 4164 and "A8" on the 41256? It's the two possible states of that pin multiplied by the two multiplexed states of the address bus that make the 256k chip capable of addressing four times as much memory as the 64k one. And for that to work your computer's motherboard circuitry needs to manipulate that pin, there's no chip out there that can magically give you more memory using just the A0-A7 that's on the 4164's package.

    If Sanyo sold a version of that machine that came with 640k soldered to the motherboard instead of 256k it's possible the motherboard already has the circuitry on it to drive that extra address line and you just need to figure out how to enable it, but if they didn't then you're looking at reverse engineering the parts of the motherboard circuitry that selects whether memory is present at a given location and the multiplexing circuitry that needs to take the 18 bit memory address that's generated by the processor to access a location within 256k and translate it into two 9-bit Row/Column strobes. (That circuitry presumably only supports 16 bit addresses now.)

    The Sanyo's circuitry probably isn't particularly unique as computers of that era goes, but I'm not sure how someone could walk you through how to hack it unless they had the same thing in front of them, or at least a good tech manual.


    dram_16_64_256.gif
    Last edited by Eudimorphodon; October 16, 2020, 09:27 AM.

    Leave a comment:


  • T-Squared
    replied
    I seem to have a winner. Checking over the statistics between the two chip types that I have, they have exactly the same pinout. (Different labels for identical pins, though, i.e. VDD = VCC)

    The current memory in the board: Mitsubishi M5K4164ANP-15: https://datasheetspdf.com/pdf-file/1...5K4164ANP-15/1

    The memory I plan to use: Texas Instruments TMS4256-15NL: https://pdf1.alldatasheet.com/datash...4256-15NL.html

    Leave a comment:


  • T-Squared
    started a topic Original-IBM-5150 or IBM-Clone Memory Experimentation Thread

    Original-IBM-5150 or IBM-Clone Memory Experimentation Thread

    Since the original thread about my copy of IRCjr complaining about text formatting and memory count got off-track, I decided to start a new thread about those who wanted to upgrade their IBM 5150 or IBM Clone system.

    For me, you've probably heard a lot about my Sanyo MBC-775, and my efforts to get it working, on this forum. Unfortunately, the system, despite its uniqueness, is not very well-equipped to handle programs made for the original system or other IBM clones. The MBC-775 only has 256k of memory and two ISA slots. Combinations of cards allow me to do certain things with the system, of course, but the fact that it only has two slots means I often have to sacrifice an ability in order to do something else. Even moreso when I have dedicated one of those slots for a XT-IDE card.

    For example, if I want to go onto the internet, to websites formatted especially for vintage low-end systems, I have an ethernet card to do so. However, if I want to listen to music or Adlib/Sound-Blaster-based sounds on the system, I have to swap the card out for a Sound Blaster. If I want to play with 16-color-based programs, I could either use a game's specially-made artifact-color mode, or (hopefully) swap in an EGA card (if it plays nice and does what I hope it will do, that is, output full 16 colors to the internal monitor).

    In this case, a dedicated 640kb memory expansion card is out of the question, as it gets rid of a chance for more color, sound, and communication capabilities for the computer. Thus, my idea was to desolder the existing RAM and replace them with sockets. If it works, this is a triple benefit, as not only have I been having intermittent problems with the RAM (only once so far), but I can expand the RAM to 1 MB (adding expanded memory for DOS in the process) for 640kb-requirement games and programs, as well as replace failed memory in the future easily.

    What I'm hoping is that 64kb memory is pin- and interface-compatible, so I simply have to plug the chips in without modification (even then, I wouldn't know what to modify).
    Last edited by T-Squared; October 16, 2020, 08:48 AM.
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