Since I had the old RCA UT4 monitor program working with the MicroVIP for initial testing, I was trying to think of a way of keeping it and maybe having some kind of dual-boot scheme.
Well, I figured out a way. There is a push button on the FPGA card that can be used. I made some changes to the FPGA code to boot the UT4 ROM if the button is pressed when coming out of reset. Otherwise, the MicroVIP ROM will boot.
To use UT4, connect a USB to TTL adapter (3.3V), and TeraTerm with a setting of 300bps 7N1. Hold the push button on the FPGA card (near the programming connector) and flip the run switch to RUN. Press <CR> in TeraTerm and the UT4 prompt (*) will appear.
This is a summary of the 3 commands in UT4:
?Maaaa cc = display cc bytes of memory starting at address aaaa
!Maaaa bb [bb]... = write byte, or several bytes starting at address aaaa
$Paaaa = run a program starting at address aaaa with X,P=R0
Note, my 1802 assembler generates listing files (.lst) that are compatible with UT4. So you just send the list file to UT4 with TeraTerm (Send File...) to load a program.