R.5.2
SEL-421 Relay Reference Manual Date Code 20111215
SEL Communications Protocols
Software Protocol Selections
Note that the relay must assert the RTS pin to provide power for some
modems, fiber-optic transceivers, and hardware protocol converters that are
port powered. Check the documentation for any port-powered device to
determine if the device supports hardware handshaking or if you must always
assert RTS (RTSCTS := N) for proper operation.
Data Frame
The relay ports use asynchronous data frames to represent each character of
data. Four port settings influence the framing: SPEED, DATABIT, PARITY,
and STOPBIT. The time allocated for one bit is the reciprocal of the SPEED.
For example, at 9600 bits per second, one bit-time is 0.104 milliseconds (ms).
The default port framing uses one start bit, 8 data bits, no parity bit, and one
stop bit. The transmitter asserts the TXD line for one data frame, as described
in the following steps:
The TXD pin is normally in a deasserted state.
➤ To send a character, the transmitter first asserts the TXD pin for
one bit time (start bit).
➤ For each data bit, if the bit is set, the transmitter asserts TXD
for one bit time. If the bit is not set, it deasserts the pin for one
bit time (data bits).
➤ If the PARITY setting is E, the transmitter asserts or deasserts
the parity bit so that the number of asserted data bits plus the
parity bit is an even number. If the PARITY setting is O, the
transmitter asserts or deasserts the parity bit so that the number
of asserted data bits plus the parity bit is an odd number. If the
PARITY setting is N, the data frame does not include a parity
bit.
➤ At the completion of the data bits and parity bit (if any), the
transmitter deasserts the line for one bit time (stop bit). If
STOPBIT is set to 2, the transmitter deasserts the line for one
more bit time (stop bit).
➤ Until the relay transmits another character, the TXD pin will
remain in the unasserted state.
Software Protocol Selections
The SEL-421 supports the protocols and command sets shown in Tab le 5.2.
Table 5.2 Supported Serial Command Sets (Sheet 1 of 2)
PROTO
Setting Value
Command Set Description
SEL SEL ASCII Commands and responses
SEL SEL Compressed ASCII Commands and comma-delimited
responses
SEL SEL Fast Meter Binary meter and digital element com-
mands and responses
SEL SEL Fast Operate Binary operation commands
SEL SEL Fast SER Binary SER commands and responses
MBA or MBB SEL M
IRRORED BITS
®
communications
Binary high-speed control commands
To Next Page
Loading...
