Date Code 20090730 Instruction Manual SEL-734 Meter
Appendix G
MIRRORED BITS Communications
Overview
MIRRORED BITS
®
is a direct meter-to-meter communications protocol that
allows meters to exchange information quickly and securely, and with
minimal expense.
The SEL-734 supports two M
IRRORED BITS channels, differentiated by the
channel specifiers A and B. Bits transmitted are called TMB1x through
TMB8x, where x is the channel specifier (e.g., A or B), and are controlled by
the corresponding SEL
OGIC
®
control equations. Bits received are called
RMB1x through RMB8x and are usable as inputs to any SEL
OGIC control
equations. Channel status bits are called ROKx, RBADx, CBADx and LBOKx
and are also usable as inputs to any SEL
OGIC control equations. Further
channel status information is available via the COM command. If both the A
and B M
IRRORED BITS channels are active, the COM A or COM B
commands must be used to distinguish which channel is displayed.
Operation
Message Formatting
MIRRORED BITS communications protocol options include MBA and MBB for
standard M
IRRORED BITS communications and MB8A/MB8B for special
message formats required with radios and some CSU/DSU devices.
M
IRRORED BITS communications messages consist of four characters or bytes.
Each byte is made up of a start bit, six data bits, one parity bit, and one or two
stop bits. The MBA/MBB settings protocol includes one stop bit, for a total of
nine bits per character. The MB8n protocol setting includes two stop bits, for a
total of 10 bits per character. Use the MB8n setting with communication
channel equipment that counts bits and requires a 10-bit character.
Message
Transmission
All messages are transmitted without idle bits between characters. Idle bits are
allowed between messages.
➤ At 4800 baud, one message is transmitted each 1/2 power
system cycle.
➤ At 9600 baud, one message is transmitted each 1/4 power
system cycle.
➤ At 19200 and 38400 baud, one message is transmitted each 1/4
power system cycle for the SEL-734.
Courtesy of NationalSwitchgear.com
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