10-6
Serial Port Communications and Commands
Date Code 20011205
SEL-311B Instruction Manual
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 M
IRRORED
B
ITS
.
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
commands, 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
handshaking is enabled) when the relay input buffer drops below 25 percent full.
The relay transmits XOFF (ASCII hex 13) when the buffer is over 75 percent full. If
hardware handshaking is enabled, the relay deasserts the RTS output when the buffer is
approximately 95 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 the XON/XOFF protocol to control the relay during data transmission. When
the relay receives XOFF during transmission, it pauses until it receives an XON character. If
there is no message in progress when the relay receives XOFF, it blocks transmission of any
message presented to its buffer. Messages will be accepted after the relay receives XON.
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