DECMCM—Set/Reset Modem Control Mode

Enables (set) or disables (reset) modem control.

Format

CSI
9/11
?
3/15
9
3/6
9
3/6
h
6/8
Enable Modem Control
CSI
9/11
?
3/15
9
3/6
9
3/6
l
6/12
Disable modem control - default

Description

When enabled for the Comm2 connector, no data is transmitted or received unless DSR is asserted. Assertion of DSR alone is sufficient to establish a connection. Loss of DSR causes a disconnect. When DSR is not asserted, no data is transmitted, and incoming receive data is ignored. When DSR is again asserted, the communications state is re-initialized to prepare for the new connection.

When enabled for the Comm1 (25-pin EIA) connector, the terminal does not transmit unless CTS is asserted. If a connection has not been established (DSR is deasserted), RLSD is ignored. Transmission and reception may still occur if CTS is asserted. Assertion of CTS with DSR and RLSD asserted indicates a connection has been established. (CTS is checked last.)

When Modem Control is disabled, transmission and reception occur regardless of the state of the modem control signal. The terminal communicates using data leads only. DTR and RTS are always asserted except during an operator initiated disconnect sequence, or the input buffer reaches the 64-byte threshold when DTR flow control scheme is selected.