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Annotation of researchv10no/cmd/2500/INTERFACE, revision 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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