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  1. taylorjpt

    Modern update of the CE-158 for the TRS-80 PC-2

    Yeah, the DMA idea was just a thought. I'm looking at building a CE-158 drop in as far as the PC2 is concerned with extra functionality. Would have been done by now if it weren't for catching covid in December! I'm glad I got my 24K RAM expanders done before that else I would have been quite...
  2. taylorjpt

    Modern update of the CE-158 for the TRS-80 PC-2

    Yeah, those I know about but not a big deal to override.
  3. taylorjpt

    Modern update of the CE-158 for the TRS-80 PC-2

    There are no flip flops in the PC2 memory decode that I can see, which one are you talking about?
  4. taylorjpt

    Modern update of the CE-158 for the TRS-80 PC-2

    Has anyone tried holding the main processor in reset and writing the RAM directly via the 60 pin connector?
  5. taylorjpt

    Modern update of the CE-158 for the TRS-80 PC-2

    Timing for the interaction between the PC2 host program and the UART on the CE-158 is actually pretty slow (Relatively speaking). This capture shows the activity when writing successive bytes to the serial port: CS #1 Polling the transmit buffer every 207uS, in this case the buffer is "Not...
  6. taylorjpt

    Modern update of the CE-158 for the TRS-80 PC-2

    Thanks for the info. Really looking forward to switching from support hardware dev to what I started out wanting to do: playing with my PC2 and the plotter. That deadbug was one of the easier ones I've done. When I used to design cell phones I would deadbug new DDR/SRAM onto boards to test...
  7. taylorjpt

    Modern update of the CE-158 for the TRS-80 PC-2

    It's funny how viewing code where the PC2 doesn't understand the tokens it just replaces them with "~". Turned on the PC2 off the CE-158 and to make sure I had the right one I hit the F6 key which should be a CSAVE statement but the first character for that as well as F4 and F5 (Com setup...
  8. taylorjpt

    Modern update of the CE-158 for the TRS-80 PC-2

    The main motivations for this project are: 1. I really like to design and then build things (1720 for this board number means this is the 720th PWB design I have done) and it does not matter to me if I build more than the first one. Kind of the same motivation that has prompted me to refurbish...
  9. taylorjpt

    Modern update of the CE-158 for the TRS-80 PC-2

    Yes, $500 for a new CE-158 because I wanted it NOW so I could get my project rolling. In retrospect, I'm quite happy with my purchase and as I anticipated, this answered some questions that the schematics alone could never do and gives me the ability to test out circuit ideas before finalizing...
  10. taylorjpt

    TRS-80 PC-2 (Sharp PC-1500) regulator teardown

    Built the first new regulator board and am very happy with it. Dropout voltage in the PC1500A on/idle state is 12mV plus the schottky reverse polarity diode. Line and load regulation is better than 3mV. For the PC1500A the idle current is about 3.5mA so the original Vcc switch drive of 500uA...
  11. taylorjpt

    Modern update of the CE-158 for the TRS-80 PC-2

    You know, I've been waiting for a pendant to come out of the woodwork on the DBx moniker... I can't remember when we gave up and just used DB as the universal prefix, convincing ourselves that it stood for DsuBminiature! More than that I'm appalled at the shortsightedness of the original...
  12. taylorjpt

    Modern update of the CE-158 for the TRS-80 PC-2

    To make life easier I'm pinning out the RS232 DB9 to connect directly to a standard USB-RS232 cable so I won't need adapters for the main use case.
  13. taylorjpt

    Modern update of the CE-158 for the TRS-80 PC-2

    Just like with the SRAM modules it turns out to be cheaper to just get a bigger part and throw away half the memory: I tested the PC2 with a 256kbit OTP and it works fine. This means I don't have to deal with programming a (slightly) cheaper 256kbit SRAM and then maintaining it while the PC2...
  14. taylorjpt

    Modern update of the CE-158 for the TRS-80 PC-2

    And yes... the BOM will be a bit above the original $10 of a bare board that just copies the CE-158.
  15. taylorjpt

    Modern update of the CE-158 for the TRS-80 PC-2

    Should be pretty slick when it's done!
  16. taylorjpt

    Modern update of the CE-158 for the TRS-80 PC-2

    Looking at the mechanical stackup today: It looks like I'll be able to leverage most of the hardware and firmware from the cassette interface including the power system, LCD touch interface etc. I'm going to use the same housing as the cassette interface and shrink the DB25F for the serial...
  17. taylorjpt

    Modern update of the CE-158 for the TRS-80 PC-2

    CSAVE into the CE-158 is really fast (relativly speaking) and saves the program in a very compact form. CLOAD should be equally fast. Next task is to test SRAM emulation of the ROM which they put in a convenient socket.
  18. taylorjpt

    Modern update of the CE-158 for the TRS-80 PC-2

    Its kind of neat the way they put the code for the add ons in the add ons without having to spin up an entire new processor.
  19. taylorjpt

    Modern update of the CE-158 for the TRS-80 PC-2

    I just used CSAVEa so I could verify it was all working... binary would look like a lot of trash on the terminal. In practice you would use the faster CSAVE.
  20. taylorjpt

    TRS-80 PC-2 (Sharp PC-1500) regulator teardown

    The three pin pot on the left sets the VGG voltage and should be set to 4.70V measured at VCC relative to ground. This has to be done when the unit switched on. VGG is the memory backup voltage when the PC is off and VCC runs the display and other stuff when it is on. I've seen it take 3+...
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