Schweitzer Engineering Laboratories SEL-352-1 - Software Protocol; Sel Ascii

Date Code 20010731 Serial Port Communications and Commands 8-7
SEL-352-1, -2 Instruction Manual
Software Protocol
Software protocols consist of standard SEL ASCII, SEL Distributed Port Switch (LMD), SEL
Distributed Network Protocol (DNP) (SEL-352-2 Relay only), SEL Fast Meter, SEL Fast
Operate, and SEL Compressed ASCII. Based on the port PROTOCOL setting, the relay
activates SEL ASCII, SEL LMD, or SEL DNP protocol. SEL Fast Meter and SEL Compressed
ASCII commands are always active.
SEL ASCII
The following software protocol is designed for manual and automatic communications.
1. All commands received by the relay must be of the form:
<command><CR> or <command><CR><LF>
A command transmitted to the relay should consist of the following:
 A command followed by either a carriage return or a carriage return and line feed.
 You must separate arguments from the command by spaces, commas, semicolons,
colons, or slashes.
 You may truncate commands to the first three characters. EVENT 1 <ENTER>
would become EVE 1 <ENTER>.
 Upper- and lower-case characters may be used without distinction, except in
passwords.
2. The relay transmits all messages in the following format:
<STX><CR><LF>
<MESSAGE LINE 1><CR><LF>
<MESSAGE LINE 2><CR><LF>
.
.
<LAST MESSAGE LINE><CR><LF>
<ETX> <PROMPT>
Each message begins with the start-of-transmission character STX (ASCII character 02) and
ends with the end-of-transmission character ETX (ASCII character 03).
3. The relay indicates how full its receive buffer is through an XON/XOFF protocol.
The relay transmits XON (ASCII hex 11) when the buffer drops below 40 percent full.
The relay transmits XOFF (ASCII hex 13) when the buffer is over 80 percent 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.