Schweitzer Engineering SEL-351P, Quick Start Manual

Page: 491 / 674

Date Code 990215 Serial Port Communications and Commands 10-7
SEL-351P Manual Técnico
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.
SEL ASCII Protocol
SEL ASCII protocol is designed for manual and automatic communications.
1. All commands received by the control must be of the form:
<command><CR> or <command><CRLF>
A command transmitted to the control 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 recloser control.
2. The SEL-351P serial port 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 control implements XON/XOFF flow control.
The serial port transmits XON (ASCII hex 11) and asserts the RTS output (if hardware hand-
shaking enabled) when the serial port input buffer drops below 25% full.
The serial port transmits XOFF (ASCII hex 13) when the buffer is over 75% full. If
hardware handshaking is enabled, the serial port 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 serial port sends
XON.
4. You can use the XON/XOFF protocol to control the SEL-351P during data transmission.
When the serial port receives XOFF during transmission, it pauses until it receives an XON
character. If there is no message in progress when the serial port receives XOFF, it blocks
transmission of any message presented to its buffer. Messages will be accepted after the
serial port receives XON.