Schweitzer Engineering Laboratories SEL-734 - Table F.4 01 H Read Coil Status Commands; Table F.5 Meter Responses to 01 H Read Coil Query Errors

F.3
Date Code 20090730 Instruction Manual SEL-734 Meter
Modbus RTU Communications Protocol
Modbus RTU Communications Protocol
Note that the meter coil addresses start at 0 (e.g., Coil 1 is located at address
zero). The coil status is packed one coil per bit of the data field. The Least
Significant Bit (LSB) of the first data byte contains the starting coil address in
the query. The other coils follow towards the high order end of this byte and
from low order to high order in subsequent bytes.
To build the response, the meter calculates the number of bytes required to
contain the number of bits requested. If the number of bits requested is not
evenly divisible by eight, the meter adds one more byte to maintain the
balance of bits, padded by zeroes to make an even byte.
The meter responses to errors in the query are shown in Table F.5 .
The 01h Read Coil assignments are the same as those in Tab le F.1 5.
02h Read Input
Status Command
Use function code 02h to read the On/Off status of the selected bits (inputs).
You can read the status of as many as 2000 bits per query. Note that the input
addresses start at 0 (e.g., Input 1 is located at address zero).
The input status is packed one input per bit of the data field. The LSB of the
first data byte contains the starting input address in the query. The other inputs
follow towards the high order end of this byte, and from low order to high
order in subsequent bytes.
Table F.4 01h Read Coil Status Commands
Bytes Field
Requests from the master must have the following format:
1 byte Slave Address
1 byte Function Code (01h)
2 bytes Address of the First Bit
2 bytes Number of Bits to Read
2 bytes CRC-16
A successful response from the slave will have the following format:
1 byte Slave Address
1 byte Function Code (01h)
1 byte Bytes of data (n)
n bytes Data
2 bytes CRC-16
Table F.5 Meter Responses to 01h Read Coil Query Errors
Error Error Code Returned
Communication
Counter Increments
Invalid bit to read Illegal Data Address (02h) Invalid Address
Invalid number of bits to read Illegal Data Value (03h) Illegal Register
Format error Illegal Data Value (03h) Bad Packet Format
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