CAI 700M - Page 186

700M HFID 6-2-15
186
Code 04
This function code is used to read from 1 to 125 contiguous input registers in a remote
device. The Request PDU specifies the starting register address and the number of registers. In
the PDU, registers are addressed starting at zero. Therefore input registers numbered 1-16 are
addressed as 0-15.
The register data in the response message are packed as two bytes per register, with the binary
contents right justified within each byte. For each register, the first byte contains the high-order
bits and the second byte contains the low-order bits.
Request
Function Code
1 Byte
0x04
Starting Address
2 Bytes
0x0000 to 0xFFFF
Quantity of Input Registers
2 Bytes
0x0001 to 0x007D
Response
Function Code
1 Byte
0x04
Byte Count
1 Byte
2 x N*
Input Registers
N* x 2 Bytes
*N = Quantity of Registers