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Annotation of researchv10no/cmd/2500/INTERFACE, revision 1.1.1.1

1.1       root        1: From kahrs Thu Oct 15 13:09 EDT 1987
                      2: To: andrew ejs td tom
                      3: Subject: Short documentation for the RS232<->RS422 card
                      4: 
                      5: Documentation for the RS232 to RS422 (and vice versa) converter
                      6: 
                      7: The converter itself is straightforward.  It receives RS-232 as a null modem
                      8: and transmits RS-422.  The reverse path is identical; it receives RS-422 as
                      9: a null modem and transmits RS-232.  If the RS-232 cable is disconnected, the
                     10: transmitters on the RS-422 side will be disabled (i.e., the transmitters
                     11: depend on carrier detect).  This permits multiple transmitters to be
                     12: connected on the same line.
                     13: 
                     14: There are two points specific to the Sony VTR.
                     15: 
                     16: First, there is a seven position DIP switch on the card; the first four
                     17: switches put 100 ohm termination resistors on the RS-422 inputs and outputs.
                     18: They are not being using currently.  The last switch (7) is the "priority in"
                     19: line; this is pulled up inside the Sony interface.  By turning the switch "on",
                     20: the line is grounded.  This permits the RS-232 line to send commands to the
                     21: Sony; otherwise they will be ignored.  This is currently "on".
                     22: 
                     23: Second, the power connector is "designed" to be connected to the Sony
                     24: REMOTE-1 connector.  Unlike the AT&T Teletype, Sony planned on external devices
                     25: and provided power.  Therefore, the interface must be provided with +5,+12 and -12
                     26: volts.
                     27: 
                     28: 

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