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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.

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