I told you guys that I would update you on my PiBM-5150 project. I figured out the hard way that my USB to DB-25 cable wouldn't cut it. Seems it is for printers and no matter how hard I tried it wouldn't work because of the path of the wires. After researching, it is apparent that the GPIO pins on the pi are configured for serial by default but it requires a little voltage change from TTY to RS-232. Rather than do like one of the videos I saw and solder junk to a bread board, I found a serial (rs-232) shield and 9pin output for the pi. Now, both computers are true rs-232 each. Instead of using a modem between them, I bought a null modem cable (crossover of Tx Rx signals) to interface the two machines directly. I'll update this evening to show it hopefully working.