Beijer Electronics NA-9379 - Manual (Page 63)

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MODBUS Programmable I/O NA-9379 FnIO S-Series
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A.3.4. 4 (0x04) Read Input Registers
This function code is used to read from 1 to approx. 125 contiguous input registers in a remote device. The
Request PDU specifies the starting register address and the number of registers. 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 contains the low order bits.
• Request
Field name Example RTU ASCII ASCII (bus line)
Start of Frame - t1-t2-t3 “,” 0x3A
Slave Address 0x07 0x07 “07” 0x30, 0x37
Function Code 0x04 0x04 “04” 0x30, 0x34
Starting Address Hi 0x00 0x00 “00” 0x30, 0x30
Starting Address Lo 0x00 0x00
“00”
0x30, 0x30
Quantity of Register Hi 0x00 0x00 “00” 0x30, 0x30
Quantity of Register Lo 0x02 0x02 “02” 0x30, 0x32
Error Check (CRC/LRC) - 0x71, 0xAD
“F3”
0x46, 0x33
End of Frame - t1-t2-t3 CR, LF 0x0D, 0xA
• Response
Field name Example RTU ASCII ASCII (bus line)
Start of Frame - t1-t2-t3 “,” 0x3A
Slave Address 0x07 0x07 “07” 0x30, 0x37
Function Code 0x04 0x04 “04” 0x30, 0x34
Byte Count 0x04 0x04 “04” 0x30, 0x34
Input Register #0 Hi 0x00 0x00 “00” 0x30, 0x30
Input Register #0 Lo 0x80 0x80 “80” 0x38, 0x30
Input Register #1 Hi 0x00 0x00 “00” 0x30, 0x30
Input Register #1 Lo 0x00 0x00 “00” 0x30, 0x30
Error Check (CRC/LRC) - 0x9C, 0x6C “71” 0x37, 0x31
End of Frame - t1-t2-t3 CR, LF 0x0D, 0xA
- In case of address 0x0000, 0x0001 input register value: 0x0080, 0x0000.