I have extra PCBs if you are interested, and i can share the schematic, I have since made more revisions to the design and the PCBs, adding an extra column of buttons, and connecting the RS-232 hardware control lines, and adding jumpers to connect/disconnect the USB UART IC to allow the RS-232 port ...

Awesome thank you! Tons of good information, i will keep all that in mind for sure. I had slowly been going back though and trying to improve my code, i removed a ton of LDAs and ANDs and used the BIT instructions instead, and i definitely understand the importance of commenting everything, it would ...

I had originally planned to have the hardware flow control pins wired up, at this point i am not entirely sure why i omitted them, i will surely be wiring them in if make a new version, so far i have been able to receive data at 19200 baud fairly reliably and write it to ram using the code below. I ...

Got it, that makes sense, has to be the issue, i am certain that the RS-232 worked before adding the MCP2221 circuitry. I had questioned it numerous times but after i already had the board out to be made, i will test removing the MCP2221, and will most likely add pin headers/jumpers to switch them ...

So it looks like it is wired correctly, i am seeing data at the 65c51 RX pin when transferring with both rs-232 and USB UART. However i noticed that the amplitude of the signal is lower when sending data over the rs-232, not getting pulled as close to ground as with the USB UART, so maybe it is not ...

According to 232 pinouts pin 3 of DB9 is TX, confirmed data at this pin with the scope, has to be something obvious i missed

EDIT: Black and white schematics

I have -9v on the TX line, and 5v on the TTL side of the MAX232, however i think i found my issue, the -9v is on pin 2 of my DB9 connector, looks like i must have swapped the tx and rx lines at the connector. I think there was some confusion because with the USB UART the tx gets connected to RX, so ...

So i realized i hadn't tested the RS-232 port at the time of posting, just did and it doesnt seem to work, it worked in the previous prototype before i added the USB UART chip, i seem to have overlooked isolating the signals, probably should have added header pins and jumpers to select between USB ...

So after seeing the Ben Eater 6502 series on youtube i was hooked, and interested to learn more, designed my own board, and i am now on my 4th revision of a 65C02 SBC, being proud of my achievement, figured this would be a good place to share. I have no formal background in electronics or ...