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System Overview
S E N D
RCV
CPU to Terminal - DSR On (CTC1)
This interface type is similar to CTB1 discussed above. A CPU port is connected to the Node M
channel interface; a terminal is connected to the Node S channel interface. Signals RTS (Request
to Send) and DCD (Data Carrier Detect) are SEND control signals sent into the channel interface;
the program plug also returns the state of Request to Send back to the port or terminal as CTS
(Clear to Send). The RTS input becomes output DCD (Data Carrier Detect) at the opposite-end
channel interface; SEND control signal DTR (Data Terminal Ready) becomes RCV Control sig-
nal DSR (Data Set Ready) at the opposite-end channel interface. DTR is forced On by the system,
so that output DSR is always On. Transmission is controlled by the state of RTS at either end; if
either the terminal or the CPU port needs to transmit data, RTS must be On before transmission
can begin.
S E N D
RCV
CPU to Private Line Modem (CPL1)
In this interface type, a CPU port is connected to the Node M channel interface; the Node M chan-
nel interface is set for DCE. The Node S channel interface is connected to a modem link, which
in turn is connected to a terminal at some remote site; the Node S channel interface must be set
for DTE for proper communications with a modem. SEND control RTS (Request to Send) at
Node M is RCV control RTS at Node S; SEND control DTR (Data Terminal Ready) is RCV con-
trol DTR at Node S (because a DTE device at Node M is communicating with a DCE device at
Node S, no "crossover" of signals is required in this interface type). SEND control DCD (Data
Carrier Detect) at Node S is RCV control DCD at Node M; SEND control DSR at Node S is RCV
control DSR at Node M. The program plug settings at Node M return the state of RTS to the CPU
port as control CTS (Clear to Send).
CPU/TERM - DSR ON
NODE M
: RTS
DTR
: DCD
DSR
CPU/PL MODEM
NODE M
: RTS
DTR
: DCD
DSR
NODE S
RTS
DTR
DCD
DSR
NODE S
DCD
DSR
RTS
DTR
036R660-000, Issue 10
2-27
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