Schweitzer Engineering Laboratories SEL-321 - Additional Software Protocol (SEL-321-1 Relay Only)

3-2 Communications Date Code 20011026
SEL-321/321-1 Instruction Manual
2. The relay transmits all non-interactive messages in the following format:
<STX><CR><LF><MESSAGE LINE 1><CR><LF>
<MESSAGE LINE 2><CR><LF>
.
.
<LAST MESSAGE LINE><CR><LF><ETX><STX> <PROMPT><ETX>
Each message begins with the start-of-transmission character STX (ASCII character 02) and
ends with the end-of-transmission character EXT (ASCII character 03). Each line of the
message ends with a carriage return and line feed.
3. The relay indicates the volume of data in its received buffer through an XON/XOFF
protocol.
The relay transmits XON (ASCII hex 11) when the buffer drops below one-quarter full.
The relay transmits XOFF (ASCII hex 13) when the buffer is over three-quarters full.
Automatic transmission sources should monitor for the XOFF character so they do not
overwrite the buffer. Transmission should terminate at the end of the message in progress
when XOFF is received and may resume when the relay sends XON.
4. You can use an XON/XOFF procedure to control the relay during data transmission. When
the relay receives an XOFF command during transmission, it pauses until it receives an
XON command. If there is no message in progress when the relay receives an XOFF
command, it blocks transmission of any message presented to its buffer.
The CAN character (ASCII hex 18) aborts a pending transmission. This is useful in
terminating an unwanted transmission.
5. Control characters can be sent from most keyboards with the following keystrokes:
XON: <CTRL>Q (hold down the Control key and press Q)
XOFF: <CTRL>S (hold down the Control key and press S)
CAN: <CTRL>X (hold down the Control key and press X)
Additional Software Protocol (SEL-321-1 Relay Only)
The SEL-321-1 Relay includes additional software protocol which supports limited multidrop,
fast meter, and compressed ASCII. Refer to Appendix G for more information on the additional
protocols.