Eaton easyE4 Manual page 638

10. Connection to other devices
10.2 Modbus TCP
10.2.2.1 Read Coils 0x01:
634
a. Byte 0 contains the request's function code
b. The remaining bytes are function-specific
If an error occurs, the Modbus TCP server will send an error message
Error-Frame
l
a. Byte 0 always contains the request's error code (0x80 + function code)
b. Byte 1 contains the exception code (error-specific)
Following is a description of the request & response function codes for each of the func-
tion descriptions in the table above:
This function reads the entered number of bit outputs starting from a specified starting
address and then returns the result in bytes (8 outputs per byte)
Table 111: Request-PDU
Function Code 1 byte
Start address 2 byte
Number of out- 2 byte
puts
Response to the request being received
1. The starting address is analyzed (distributed among bytes 1 and 2)
a. Byte 1 = Hi; Byte 2 = Lo
2. The number of outputs is analyzed (distributed among bytes 3 and 4)
a. Byte 3 = Hi; Byte 4 = Lo
3. The output states are read
a. From the start of the (starting address) to (starting address + number of
outputs)
Table 112: Response-PDU
Function Code 1 byte
Bye Count 1 byte
Output values n * 1 byte
n= Number of outputs read / 8
Preparation for sending the response
1. The read bits are encoded in bytes
(1 but per output state; 1=ON, 0=OFF)
2. The LSB of the first byte, i.e., bit 0, contains the state of the output that is
addressed first in the request. The other outputs follow in ascending order.
easyE4 10/19 MN050009 EN www.eaton.com
0x01 ;Read Coils
Must always be 1 less than the starting output you want
(zero-based)
1 to 2000 (0x7D0)
0x01 ;Read Coils
N
Value