I realized I need to use the pointer register to override both the destination and source register. I've finished writing a piece of code which grabs a string from ROM and puts it out to the UART. I use an index variable to the string. So I want to copy that to the pointer register, and then copy the pointer data (the ROM character) to the UART. I can't do it easily in the TTL version because that would mean putting the source and destination and the pointer address to the same bus. So the source and destination would drive onto the same bus at the same time. But I think I will need it. This is why I wanted to start writing some software. You find out very quickly what you need in the hardware when you start writing.