The USRobotics Courier 2400 Modem uses pin 12 of the RS-232C to indicate 'High Speed' to the computer. When it is set at the 2400 baud rate, (default), the HS LED in the front goes on and pin 12 of the RS-232C interface goes high. The RS-232C interface of the TRS-80 Model 4 does not recognize pin 12 at all: it is connected to ground. When the Courier sends the HS signal, the TRS-80 Model 4 sends it to ground, pin 12 goes low, and the HS LED does not go on. However, transmission is not affected. An eassy cure to have the HS LED function properly is to remove the wire that connects pin 12 at either end of the cable. Luis M. Garcia-Barrio, 8/N/1 #004 (215-848-5728).