IBM 3708 Description page 61

For lines operating with the CDSTL option, the 3708 waits for RI before activating
DTR. Once DTR has been activated, DSR must be presented within 20 seconds or
a line error is reported. For switched lines and nonswitched lines, if DSR drops
after it has become active, the 3708 breaks the connection.
Pin 7 - Signal Ground
Pin 8 - DCD - Data Carrier Detect (3708 input) For lines that do not use PRTS,
normally HDX communication facility, the 3708 will make sure that DCD is not
present before transmitting. If DCD is present, it indicates that the line has not been
turned around and that the remote device is still transmitting.
For lines with PRTS, when the Auto On-Hook option is specified, the 3708 detects
the loss of DCD and breaks the connection.
Pin 15 - TxC - Transmit Clock (3708 input) This pin is used only for SDLC
connections specifying external clocking. It provides the baud rate clock for
transmitted data (TxD).
Pin 17 - RxC - Receive Clock (3708 input) This pin is used only for SDLC
connections specifying external clocking. It provides the baud rate clock for received
data (RxD).
Pin 18 - TC - Test Control This pin is not used by the 3708.
Pin 20 - DTR - Data Terminal Ready (3708 output) This pin is used by the 3708 to
indicate that a connection should be established or maintained. The 3708 drops
DTR whenever disconnecting.
For nonswitched lines, DTR is activated when the line is enabled and maintained
until a line error is detected or the connection is broken by the host.
For switched lines not using CDSTL, DTR is activated when the line is enabled.
For lines using CDSTL, DTR is not activated until RI has been detected. Once the
connection is established, DTR is maintained until a line error is detected or the
connection is broken by the host.
Pin 22 - RI - Ring Indicate (3708 input) This pin provides a signal from the modem
indicating an incoming call. RI is monitored by the 3708 when the CDSTL option is
selected. Once RI is presented, the 3708 activates DTR and wait for DSR to
complete the connection.
Pin 23 - DRS - Data Rate Select This pin is not used by the 3708.
Pin 24 - DTE transmit clock (3708 output) When the 3708 is providing clock, it
outputs the baud rate clock on pin 24. This is used for SDLC when the internal
clock option is selected.
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IBM 3708
Description