6100 BSC Programming Manual

6100 BSC Link and Station Management
several times above, BSC expects DSR to appear within a certain
interval (BSCCONNECTO). Thereafter, DSR must stay on throughout
the connection, and it may stay on even if the application makes
a disconnect request. BSC doesn't monitor DSR between requests,
but if it drops during a request, the request completes with a
modem error.
If the line is switched, the modem asserts DSR in response to
DTR. When an application requests a connection, BSC expects DSR
to appear within a certain interval (BSCCONNECTTO). Thereafter,
DSR must stay on throughout the connection. If DSR drops, BSC
drops DTR and reports an error. (If a request was in progress,
that request completes with a modem error; if not, the subsequent
request completes with a modem error.) If the application makes
a request to disconnect the line, BSC expects DSR to drop within
a certain interval (BSCDISCONNECTTO).
The timeout intervals are SYSGEN parameters, described in
Section 1. You can also change them with CMI or the SET
CONFIGURATION request.
Request to Send (RTS)
The use of this signal depends on whether the line is full duplex
(a four-wire circuit) or half duplex (a two-wire circuit).
If the line is full duplex, RTS is on whenever DTR is on, and off
whenever DTR is off.
If the line is half duplex, RTS is on whenever the station is
attempting to write. To overlap line turnaround with processing,
BSC raises RTS after any READ, WRITE, or WRITEREAD request,
except one that disconnects the line or returns it to CONTROL
state. Figure 2-8 demonstrates the reason for this strategy.
Notice that whether the next request is a READ, a WRITE, or a
WRITEREAD, the first action is a write: a WRITE or WRITEREAD
request sends a message to the remote station, while a READ
request sends an acknowledgement or an EOT. If the next request
is CONTROL, it also begins with a write, whether the sequence is
TTD, WACK, or DLE EOT. By anticipating the need for RTS, instead
of simply reacting to requests, BSC lessens the impact of line
turnaround delay on the application.
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