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Thread: Godbout Interfacer 1 stops Imsai´s front panel...

  1. #1

    Default Godbout Interfacer 1 stops Imsai´s front panel...

    Hello.

    I own godbout interfacer 1 serial card. When i mount it to my imsai 8080 motherboard, i cannot examine or deposit anymore. Imsai seems to be blocked out. Now, with my logic probe, i checked the 74xx logic chips, they seem to be fine. Which signal on S100 can stop the system ? First, i thought, one of the databus driver is damaged, but they look fine on logic probe. Do you have an idea ?

    thx

    Jan

  2. #2
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    Default

    The IMSAI front panel has incompatible signals with IEEE S-100 compatible cards.
    Many cards have ways to disable the offending signals, you'll have to check the Interfacer 1 manual to
    see if they can be disabled.

  3. #3

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    Quote Originally Posted by Jan1980 View Post
    Hello.

    I own godbout interfacer 1 serial card. When i mount it to my imsai 8080 motherboard, i cannot examine or deposit anymore. Imsai seems to be blocked out. Now, with my logic probe, i checked the 74xx logic chips, they seem to be fine. Which signal on S100 can stop the system ? First, i thought, one of the databus driver is damaged, but they look fine on logic probe. Do you have an idea ?

    thx

    Jan
    I believe you had DRAM. What kind of DRAM board do you have. Many don't do real refresh, controlled by the CPU. Things like interrupts from the serial card can cause the DRAM to stop refreshing. You can put clear tape on pins to mask them. I put it so the tape is on the fiberglass edge of the board's connector, so that the clean edge is at the edge of the connector, and then use razor to trim it to the width of the pin to remove the excess. I then plug it into the mother board. This allows you to easily isolate a pin you think may be an issue. You can remove the tape easily later. Just don't leave it on the pin for 5 years.
    Dwight

  4. #4

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    Looking at the interfacer 1 manual, I don't see anything that should be an issue. The only driven signals onto the bus are the data lines and the interrupts.
    Dwight

  5. #5
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    Quote Originally Posted by Dwight Elvey View Post
    The only driven signals onto the bus are the data lines and the interrupts.
    Dwight
    Did you check the extra ground pins?

  6. #6

    Default

    The CompuPro Interfacer 1 as well as most other CompuPro boards were designed to meet the IEEE696/S100 standard. This causes a problem when these boards are used in an IMSAI as Al Kossow pointed out above. CompuPro described the issue (and the solution) as follows:

    "The new IEEE 696/S-l00 bus standard calls for lines 20 and 70 to be grounded on the bus. When the IMSAI front panel was designed, many memory boards had the capability to be "protected" from accidental writes to the board. To accommodate these boards, the IMSAI front panel grounded line 70 but pulled up line 20 with a resistor that also enabled all the front panel functions. When DISK 1 [or any other IEEE696 standard S100 board] is inserted, line 20 is grounded and the front panel is disabled. The solution is to cut line 20 on the front panel since this line is now defined as ground."

    Alternatively, if you prefer not to modify the IMSAI and you don't plan to install any other IEEE696/S100 boards into it, you could cut the trace leading to line 20 on the Interfacer 1.

  7. #7

    Default

    Quote Originally Posted by Al Kossow View Post
    Did you check the extra ground pins?
    I didn't think of that, thanks for reminding me. More tape to mask pins. I would think the thin packaging tape would work well. You want it to be thin so as to not bend the socket pins.
    70 and 98 might be the only issues. Look at the charts Retrotechnology.com has.
    Dwight
    Last edited by Dwight Elvey; October 14th, 2019 at 09:50 PM.

  8. #8

    Default

    Hello.

    I tried the card without bus drivers. Then, i decided me to cut the pin 20 on the interfacer. Then, i removed bus drivers again. Always the same, frontpanel not working. Only RUN/STOP and RESET. I am using 2 Salota mixed memory cards with static RAMs. Every card has 32kb. On the card in the higher memory space are installed 2 empty 2716 eprom. One located on F000, the other located on F800. Later, i´ll use the F000 for floppy bios and the one on F800 for a small machine language monitor.
    I´ve also other memory cards in stock with dynamic RAM. Always the same. Which lines can also cut off the front panel ??

    thx

    Jan

  9. #9

    Default

    I have forget to say. Pin 20 is cutted together with Pin 70. No, i disconnected (with thin tape) Pin 98, then 99. Always the same.. FPA not working...

    thx

    Jan

  10. #10

    Default

    Quote Originally Posted by Jan1980 View Post
    I have forget to say. Pin 20 is cutted together with Pin 70. No, i disconnected (with thin tape) Pin 98, then 99. Always the same.. FPA not working...

    thx

    Jan
    You really should use tape.
    There was no reason to cut 99? Also 20 is your only ground??
    Please don't cut any more traces.
    Please this time, list what actions you did , what it actually did?
    I suspect it isn't a compatibility problem.
    It might be pin 53. Please don't cut traces.
    Dwight

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