From kahrs Thu Oct 15 13:09 EDT 1987 To: andrew ejs td tom Subject: Short documentation for the RS232<->RS422 card Documentation for the RS232 to RS422 (and vice versa) converter The converter itself is straightforward. It receives RS-232 as a null modem and transmits RS-422. The reverse path is identical; it receives RS-422 as a null modem and transmits RS-232. If the RS-232 cable is disconnected, the transmitters on the RS-422 side will be disabled (i.e., the transmitters depend on carrier detect). This permits multiple transmitters to be connected on the same line. There are two points specific to the Sony VTR. First, there is a seven position DIP switch on the card; the first four switches put 100 ohm termination resistors on the RS-422 inputs and outputs. They are not being using currently. The last switch (7) is the "priority in" line; this is pulled up inside the Sony interface. By turning the switch "on", the line is grounded. This permits the RS-232 line to send commands to the Sony; otherwise they will be ignored. This is currently "on". Second, the power connector is "designed" to be connected to the Sony REMOTE-1 connector. Unlike the AT&T Teletype, Sony planned on external devices and provided power. Therefore, the interface must be provided with +5,+12 and -12 volts.