
10.9
Date Code 20090730
Instruction Manual
SEL-734 Meter
Communications
Communications Protocols
The meter activates protocols on a per-port basis. See
in the
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, Modbus, or M
IRRORED
B
ITS
.
SEL ASCII Protocol
SEL ASCII protocol is designed for manual and automatic communications.
All commands received by the meter must be of the form:
<command> <Enter>
or
<command> <CRLF>
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 meter.
A command transmitted to the meter should consist of the command followed
by either a CR (
<Enter>
) 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 lowercase
characters may be used without distinction, except in passwords.
The meter 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.
The meter implements XON/XOFF flow control.
The meter transmits XON (ASCII hex 11) and asserts the RTS output (if
hardware handshaking is enabled) when the meter input buffer drops below
25 percent.
The meter transmits XOFF (ASCII hex 13) when the buffer is over 75 percent.
If hardware handshaking is enabled, the meter deasserts the RTS output when
the buffer is approximately 95 percent.
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
meter sends XON.
You can use the XON/XOFF protocol to control the meter during data
transmission. When the meter receives XOFF during transmission, it pauses
until it receives an XON character. If there is no message in progress when the
meter receives XOFF, it blocks transmission of any message presented to its
buffer. Messages will be accepted after the meter receives XON.
The CAN character (ASCII hex 18) aborts a pending transmission. This is
useful in terminating an unwanted transmission.
Содержание SEL-734
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