I was looking at the data sheet again and saw that although the Vss is 0v and the Vdd is -9v, Vih is from -1v to Vss (nom 0v) and Vil is from Vdd (nom -9v) to -4v. So the minimal difference between Vih and Vil is -4 to -1, which is a 3 volt swing, and not the 9v I originally thought.

If I shift all this up to positive voltages (because the negatives hurt my head) then we have Vss of 9v, Vdd of 0v, Vih of 8-9v and a Vil of 0-5v.

If I hook up an 8052 with a Vcc of 9v and a Vss of 4v, then its logic swings should do highs of (roughly) 9v and lows of 4v, which should be within the threshold of the logic in the TMS6100.

Does that sound right? Is that basically what you said, Lynn, with the relative voltages shifted up?

Could you repeat that part about the series resistors and how they would help with low output signals from the TMS6100 which would probably go below 4v?

Thanks so much for the help.

-Sam