Com Port Interface Controls - Cabletron Systems FRX6000 Maintenance Manual

COM Port Interface Controls

DTR and RTS are disabled when the FRX6000 issues a bus reset on
power-up. When the node is ready to begin using the serial interface,
DTR and RTS will be raised high.
While the system is running, DSR is used to indicate that the
equipment attached to the node is ready. While DSR is ON, the node
accepts input and produces output on the serial interface. While DSR
is OFF, the node stops output and ignores input on the interface. The
response time of the node (from DSR turning OFF until serial input/
output stopping) is one second or less.
Within one second of DSR turning ON, the node resumes output and
begins accepting input (based on 9600 bps-if serial I/O is slower, it
will take proportionately longer). In operation, the node will finish
output of the screen in progress, then look at DSR; if it is OFF, no
new output will occur. The effect is that when DSR changes from
ON to OFF, serial output might produce a full screen of characters
before stopping. This accounts for the time of one second or less at
9600 bps. The speed of the serial output, and any XOFF/XON, could
extend the time to finish the screen in progress after DSR goes OFF.
If DSR has momentary changes (i.e., ON, OFF, ON), input and
output will be interrupted, and input characters will be discarded.
This case is seen in situations where DSR is left unconnected or is
not driven. In such circumstances there is a possibility of noise
pickup on DSR. To avoid this, connect DSR to a definite signal so a
level will exist on DSR in cases where it would otherwise be uncon-
nected. If no signal is supplied by the terminal equipment, connect
DSR directly to DTR on the COM1 interface with an industry-
standard null modem.
The FRX6000 ignores RI and CTS signals on the COM port.
2-20 FRX6000 Maintenance Guide, Rev 03