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Thread: RTC ISA 8 bits (Very Low Profile)

  1. #11


    Quote Originally Posted by kgober View Post
    here's an example from back then of a CPU interposer design with a battery holder:
    Ahhhh, yes... Microsync dClock...
    PM me if you're looking for 3" or 5" floppy disks. EMail For everything else, Take Another Step

  2. #12
    Join Date
    May 2011
    Outer Mongolia


    Quote Originally Posted by Shadow Lord View Post
    Yes and they take far less space then this design. What is needed in the 5150/5160 class machines is a ROM (or CPU) interposer design that allows for a battery holder. Most of the "vintage/original" designs were with a self contained battery so are no good any more.
    If you don't care about the port 70h RTC functionality (which I can't imagine is very important for an XT-class machine without BIOS support) and just want a thing to set the time at boot there is a user here that makes "Smartwatch" work-alikes that have external battery holders. They use the same chip as you'd find in the old under-ROM "zero slot clocks". Whether they'd fit a given machine is going to depend a lot on the layout of the BIOS sockets, of course.

    I can speak from experience that the DS1215/1216/1315 chips used on these devices are *very* simple to design onto a board. You could probably *almost* get away with "dead-bug"-ing one along with its crystal and battery directly onto a ROM chip, although the resulting spaghetti would be pretty atrocious. It would make some real sense for someone to offer a version of the XT-IDE card that includes one. (There's nothing magical that requires it to live under a motherboard ROM, it works fine under an option ROM as well. That's how I implemented it.)
    My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs

  3. #13


    Kicad project, gerbers and SPLD files already available:

  4. #14
    Join Date
    Sep 2016
    Melbourne, Australia


    Quote Originally Posted by spark2k06 View Post
    The machine to which it is intended is an XT, and I think that not everyone has RTC unlike AT. In my case, and more specifically, I built it to use it on my Micro8088, to which I modified its BIOS to make use of it but it could be used in any XT through an application or by modifying its BIOS, in any case, using port 70h:
    My generic RTC program supports the AT clock mapping in an XT, so it should work with your card.

  5. #15


    Quote Originally Posted by David_M View Post
    My generic RTC program supports the AT clock mapping in an XT, so it should work with your card.

    I have tested your solution and for those XT systems that do not have the adapted BIOS it is perfectly valid:

    However, if Sergey's XT-CF-Lite board is used or similar:

    Select a port that does not conflict because your solution confuses it with RTC MM-58167 and does not find the true RTC of port 0x70:

    Last edited by spark2k06; December 27th, 2019 at 10:02 PM.

  6. #16
    Join Date
    Jan 2017
    Galicia, Spain


    I ordered one of these for my Turbo XT Clone. I was interested in it mainly due to its very low profile and my board does not have enough clearance around ROM chips to use another thing. Unfortunately the board uses an Acer chipset (M1101) that repurposed AT RTC I/O ports (70h & 71h) so I wasn't able to make the card work. Spark2k06 was very kind and had a lot of patience helping me to pinpoint the origin of the problem and sending a redesigned card using a different set of I/O ports (240h & 241h) to solve the problem. I have written an utility in Turbo Pascal (4.0 or higher) to configure the card. Here it is with the source code for those interested:

    I/O ports are defined as constants in the declaration section of the program. There is very little error checking but I have been using it successfully for some time. Feel free to use/improve it as you like.


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