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Great hack. Going to give this a try. I was also thinking of enhancing this by connecting the TX through the unused transceiver on U13 and then to the unused pins on the keyboard connector. This will give a bi directional 8251 "keyboard" via rs422 that I can connect to a PC. It can be used...

DJ Sures wrote: ↑Mon May 15, 2023 7:32 am So you can boot into text mode? It just goes funky in mode G2?

Missed this question earlier... text mode is bad. The screen shot I posted is text mode.

This is exactly one of the uses for the 8251A hack. You could use this for serial out for debugging by writing to 90h and 91h to display debug info. No need to switch the console using redirect.com just write to the keyboard controller to send chars out. Make sure you preserve RX enable in 91h so t...

So you can boot into text mode? It just goes funky in mode G2? If that's the case, you could put the tms99 in bitmap mode, meaning it splits the memory into 3rds. You can use NABULIB for that. A good test could be to simply draw a horizontal line across the center of each tile. Use this project: ht...

No joy in Nabu land so far. I was checking all the system DRAM outputs and they all look similar, which I assume is OK. So my initial guess of the U47, or one of the HM4864P, being bad based on the diagnostic guide and image on screen was incorrect. So I went about creating some VDP test code to see...

Well the de-solder-er arrives tomorrow, and just in time. Powered up the Nabu and I see this now.... 2023-05-11-220355.jpg Which according to Rudy's handy dandy debug manual looks like U46 - HM4864P is bad. Will do some probing around to see and pick up some replacement parts & sockets. I accide...

Thanks for all the help. Got it work tonight. The nabulib did help! My problem was the 9918 documentation labelled in the text description of the register 1 as bit 0 through 7, which i would interpret as bit 0 as the LSB. However the picture of the bits for register 1 shows bit 0 as the MSB!?!... Tu...

Thanks productiondave for the feedback. I have registered the irq handler in the vector table. Actually added unique handlers for all 8 interrupts and I'm getting the HCCA Tx interrupt if I enable it in the control register. I need to check my code again, I may be reading the VDP status at an inappr...

On a similar topic... Has anyone got the VDP interrupt to work? So far I cannot get it to fire on the Z80. I think I have done everything correctly: 1. Setup a new Vector table & update the I register 2. Set bit 3 (for VDP IRQ) in Port A of the sound chip (I/O address 41) 3. Cleared any pending ...

Question about the VDP register 1 bit 0 - the 4K/16K selection. It seems that all the ROM/BIOS out there set this bit to 0. Reading the documentation I think this should be set to 1 according to the TMS9118.PDF doc: Screenshot from 2023-05-08 10-44-52.png Am I missing something? ---- For some backgr...