Date: Monday, 2 April 1984 11:44-MST From: Dick Mead Re: USR S-100 modem. Making a sensible mod to USR's S-100 modem DTR control... The mod is simple: Above the 8251 Uart is a 7400 (IC20 I think). Careful inspection should show that pins 4,5,6 of the 7400 are not used. The diode in the center of the board, which the brief manual mentions can be removed to stop power-up off-hook at the cost of program control of DTR, needs to have the lead on the anode (8251) side made available to solder a wire to. (Replace or just resolder it). 1> Break the anode connection (only) of the diode to the 8251 (DTR line). 2> Solder a small wire from pin 6 of the 7400 to the free diode anode lead. 3> Solder a small wire to pins 4 & 5 of the 7400 (shorting them), and solder the other end to the pad where the diode anode used to go (DTR line) 4> Now writing a 1 to DTR will take mode off-hook (as it should have been) And it powers up on hook....works for me fine. You will have to invert the sense of the DTR bit in USR software now. ..Dick..