H.4
SEL-351A Relay Instruction Manual Date Code 20080213
Distributed Network Protocol
EIA-232 Physical Layer Operation
EIA-232 Physical Layer Operation
The RTS signal may be used to control an external transceiver. The CTS
signal is used as a DCD input, indicating when the medium is in use.
Transmissions are only initiated if DCD is de-asserted. When DCD drops, the
next pending outgoing message may be sent once an idle time is satisfied. This
idle time is randomly selected between the minimum and maximum allowed
idle times (i.e., MAXDLY and MINDLY). In addition, the SEL-351A
monitors received data and treats receipt of data as a DCD indication. This
allows RTS to be looped back to CTS in cases where the external transceiver
does not support DCD. When the SEL-351A transmits a DNP message, it
delays transmitting after asserting RTS by at least the time in the PREDLY
setting. After transmitting the last byte of the message, the SEL-351A delays
for at least PSTDLY milliseconds before deasserting RTS. If the PSTDLY
time delay is in progress (RTS still high) following a transmission, and
another transmission is initiated, the SEL-351A transmits the message without
completing the PSTDLY delay and without any preceding PREDLY delay.
The RTS/CTS handshaking may be completely disabled by setting PREDLY
to OFF. In this case, RTS is forced high and CTS is ignored, with only
received characters acting as a DCD indication. The timing is the same as
above, but PREDLY functions as if it were set to 0, and RTS is not actually
deasserted after the PSTDLY time delay expires.
Courtesy of NationalSwitchgear.com
To Next Page
Loading...