6100 BSC Programming Manual

6100 BSC Link and Station Management
Data Terminal Ready (DTR)
The use of this signal depends on whether the line is switched or
leased.
If the line is leased, DTR is asserted as part of the line
configuration procedure. If you specified AUTOCONF in the SYSGEN
entry for the line, CP6100 sends the line parameters to the
LIU after the line is downloaded. (See Section 3 of the
CP6100 I/O Process Programming Manual for a complete
description.) If you didn't specify AUTOCONF, the application
sends the line parameters in a SET CONFIGURATION request. DTR
stays set until you redefine the line for switched operation.
If the line is switched, DTR is asserted by application request.
There are two ways to cause DTR to be set:
• A CONTROL request with the "connect" option. BSC establishes
a modem connection by raising DTR and awaiting DSR.
• A request to write or read from the line, without a prior
CONTROL request. The request to connect--by raising DTR
and waiting for DSR--is implicit in the request to perform
the first data transfer.
There are four events that cause DTR to drop:
• A CONTROL request with the "disconnect" option. BSC severs
the modem connection by sending a DLE EOT sequence, then
dropping DTR.
• A CMI STOP request or a CLOSE call issued by the last user of
the line. Line activity stops abruptly, and DTR drops.
• An arriving disconnect sequence (DLE EOT) on a switched line.
• A modem error that causes DSR to be lost, or a connect
timeout (described below).
Data Set Ready (DSR)
The use of this signal depends on whether the line is switched
or leased.
On a leased line the modem normally sets DSR as soon as power is
applied. When an application requests a connection, as described
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