Schweitzer Engineering Laboratories SEL-351 - SEL ASCII Protocol

Date Code 20001006 Serial Port Communications and Commands 10-7
SEL-351 Instruction Manual
activates protocols on a per-port basis. The Sel-351 Relay is compatible with the SEL-DTA2
Display/Transducer Adapter. See Settings Sheet 24 in Section 9: Setting the Relay.
To select SEL ASCII protocol, set the port PROTO setting to SEL. To select SEL Distributed
Port Switch Protocol (LMD), set PROTO = LMD. To select DNP protocol, set PROTO = DNP.
SEL Fast Meter and SEL Compressed ASCII commands are active when PROTO is set to either
SEL or LMD. The commands are not active when PROTO is set to DNP or MIRRORED BITS.
SEL ASCII Protocol
SEL ASCII protocol is designed for manual and automatic communications.
1. All commands received by the relay must be of the form:
<command><CR> or <command><CRLF>
A command transmitted to the relay should consist of the command followed by either a CR
(carriage return) or a CRLF (carriage return and line feed). You may truncate commands to
the first three characters. For example, EVENT 1 <ENTER> would become EVE 1
<ENTER>. Upper and lower case characters may be used without distinction, except in
passwords.
Note:The ENTER key on most keyboards is configured to send the ASCII character 13 (^M)
for a carriage return. This manual instructs you to press the ENTER key after com-
mands, which should send the proper ASCII code to the relay.
2. The relay transmits all messages in the following format:
<STX><MESSAGE LINE 1><CRLF>
<MESSAGE LINE 2><CRLF>
.
.
.
<LAST MESSAGE LINE><CRLF>< ETX>
Each message begins with the start-of-transmission character (ASCII 02) and ends with the
end-of-transmission character (ASCII 03). Each line of the message ends with a carriage
return and line feed.
3. The relay implements XON/XOFF flow control.
The relay transmits XON (ASCII hex 11) and asserts the RTS output (if hardware hand-
shaking enabled) when the relay input buffer drops below 25% full.
The relay transmits XOFF (ASCII hex 13) when the buffer is over 75% full. If hardware
handshaking is enabled, the relay deasserts the RTS output when the buffer is approximately
95% 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.
Courtesy of NationalSwitchgear.com