ICPDAS ET-7000, User Manual, Page: 100 / 165

ET-7X00/PET-7X00 User Manual, version 1.1.2 Page: 95
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4.5. Modbus Functions and Registers
4.5.1. 01 (0x01) Read Coils
This function code is used to read the status of coils in an ET-7X00/PET-7X00 module. The
Request PDU specifies the starting address, i.e. the address of the first coil specified, and
the number of coils. In the PDU Coils are addressed starting at zero.
The coils in the response message are packed as one coil per bit of the data field. Status is
indicated as 1=ON and 0=OFF. The LSB of the first data byte contains the output addressed
in the query. The other coils follow toward the high order end of this byte, and from low
order to high order in subsequent bytes.
If the returned output quantity is not a multiple of eight, the remaining bits in the final
data byte will be padded with zeros (toward the high order end of the byte). The Byte
Count field specifies the quantity of complete bytes of data.
Here is an example of a request to read digital outputs of ET-7026/PET-7026 module:
Request Response
Field Name (Hex) Field Name (Hex)
MBAP Header
01
MBAP Header
01
02 02
00 00
00 00
00 00
06 04
Unit Identifier 01 Unit Identifier 01
Function Code 01 Function Code 01
Starting Address Hi 00 Byte Count 01
Starting Address Lo 00 Outputs status 0-1 02
Quantity of Outputs Hi 00
Quantity of Outputs Lo 02
The status of outputs 0-1 is shown as the byte value 02 hex, or binary 0000 00 10 . DO1 is in
the seventh bit position from the left, and DO0 is the LSB of this byte. The six remaining
high order bits are zero filled.