I am working on designing a Z80 computer that utilized the TMS9918ANL for graphics. I am currently just trying to make sure the TMS9918ANL is working, so I hooked up the control pins the bus (backwards as I should), power/ground, a crystal, and CSW/CSR. In order to test it without RAM, I took the RD pins and tied them to ground using 10K pull-down resistors. I was told that this should produce a black screen if I wired it correctly. Could you check over my wiring and my code to make sure I am executing this right and correctly writing to the TMS9918A's registers? I took screenshots of my schematics from Kicad and uploaded them to a Google Drive folder here (note, it says the other pins of the TMS9918A are wired up, but in my actual circuit they are unconnected and the RD pins are pulled down to ground): https://drive.google.com/drive/folders/1bNtJaH40HGuP_w_PZnNKDf3ZZJnJuWBJ?usp=sharing

And my code can be found here: https://pastebin.com/LDhyMr5r

I am very new to all of this, so I appreciate your time and understanding with my lack there of. If you can help me figure out my problem, I will be happy to send a photo of the computer printing your name in text as soon as I get it running :)

If there is anything else you need to assess my situation, please let me know. Thank you for your time and help in advance!

  • And just a note, I used the TMS9918ANL loading code from the LMC80 project. So maybe referencing the original program and circuits may be of help. Just a suggestion :) Jul 13, 2020 at 0:25
  • No TMS9918A in those screen shots. Can you upload the Kicad schematic file? Jul 13, 2020 at 10:12
  • @BruceAbbott I am currently not at home, so I can't upload the full schematic, but the screenshot of the TMS9918A is in there. Here is a link directly to the picture drive.google.com/file/d/1cY4gBT7nFVyltgDI8mptUAvP437HRQk-/… Let me know if you have any further questions. I will comment again once I have put the schematic files in there. Jul 13, 2020 at 10:23
  • @BruceAbbott The Kicad schematics are in the Google Drive folder now :) Jul 13, 2020 at 12:28
  • 1
    Some other info about the TMS9918A in case it helps anyone Jan 8, 2021 at 15:04


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