Date Code 20011009
SEL-701-1 Monitor
Modbus
®
RTU Communications Protocol
01h Read Coil Status Command
C.5
01h Read Coil Status Command
Use function code 01h to read the On/Off status of selected bits (coils). You may
read the status of up to 2000 bits per query. Note that the monitor addresses inputs from
0. The monitor returns 8 bits per byte, most significant bit first, with zeroes padded into
incomplete bytes.
To build the response, the monitor calculates the number of bytes required to
contain the number of bits requested. If the number of bits requested is not evenly
divisible by 8, the monitor adds one more byte to contain the balance of bits, padded by
zeroes to make an even byte.
Table C.4
01h Read Coil Status Command
Bytes
Field
The Master Request Must Have the Following Format
1 byte
Slave address
1 byte
Function code (01h)
2 bytes
Address of the first bit
2 bytes
Number bits to read
2 bytes
CRC-16 for message
A Successful SEL-701-1 Monitor Response Will Have the Following Format
1 byte
Slave address
1 byte
Function code (01h)
1 byte
Byte count
n bytes
Byte count bytes of data
2 bytes
CRC-16 for message
Содержание SEL-701-1
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