Eaton easyE4 - Page 796

10. easyE4 communication Connection to other devices
10.17 Modbus TCP
Read Discrete Inputs 0x02:
This function reads a specified number of bit inputs starting from a specified starting
address and then returns the result in bytes (8 inputs per byte)
Function Code
1 byte
0x02 ;Read Discrete Inputs
Start address
2 byte
Must always be 1 less than the starting input you want
(zero-based)
Number of out-
puts
2 byte
1 to 2000 (0x7D0)
Tab. 137: Request-PDU
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 inputs is analyzed (distributed among bytes 3 and 4)
a. Byte 3 = Hi; Byte 4 = Lo
3. The bit input states are read
a. From the start of the (starting address) to (starting address + number of
bit inputs)
Function Code
1 byte
0x02 ;Read Discrete Inputs
Bye Count
1 byte
N
Output values
n* 1 byte
value
Tab. 138: Response-PDU
n= Number of inputs read / 8
Preparation for sending the response
1. The read bits are encoded in bytes
Bit per input state; 1=ON, 0=OFF)
2. The LSB of the first byte, i.e., bit 0, contains the state of the input that is
addressed first in the request. The other inputs follow in ascending order.
3. If a byte is not used fully, the unused bits will be padded with 0's.
Once the response is encoded, it is sent.
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