23 (0X17) Read/Write Multiple Registers - Hitachi HX-RIO3 Series User Manual

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A.3.10. 23 (0x17) Read/Write Multiple Registers
This function code performs a combination of one read operation and one write operation in a single
MODBUS transaction. The write operation is performed before the read. The request specifies the starting
address and number of holding registers to be read as well as the starting address, number of holding
registers, and the data to be written. The byte count specifies the number of bytes to follow in the write
data field.
The normal response contains the data from the group of registers that were read. The byte count field
specifies the quantity of bytes to follow in the read data field.
•
Request
Field name
Start of Frame
Slave Address
Function Code
Read Starting Address Hi
Read Starting Address Lo
Quantity of Read Hi
Quantity of Read Lo
Write Starting Address Hi
Write Starting Address Lo
Quantity of Write Hi
Quantity of Write Lo
Byte Count
Write Reg. Value #0 Hi
Write Reg. Value #0 Lo
Write Reg. Value #1 Hi
Write Reg. Value #1 Lo
Error Check (CRC/LRC)
End of Frame
•
Response
Field name
Start of Frame
Slave Address
Function Code
Byte Count
Write Reg. Value #0 Hi
Write Reg. Value #0 Lo
Write Reg. Value #1 Hi
Write Reg. Value #1 Lo
Error Check (CRC/LRC)
End of Frame
In case of address 0x0800, 0x0801 output register value: 0x0000, 0x0000 changes to 0x1122, 0x3344.
-
Example RTU
- t1-t2-t3
0x07 0x07
0x17 0x17
0x08 0x08
0x00 0x00
0x00 0x00
0x02 0x02
0x08 0x08
0x00 0x00
0x00 0x00
0x02 0x02
0x04 0x04
0x11 0x11
0x22 0x22
0x33 0x33
0x44 0x44
- 0x88, 0x3F
- t1-t2-t3
Example RTU
- t1-t2-t3
0x07 0x07
0x17 0x17
0x04 0x04
0x11 0x11
0x22 0x22
0x33 0x33
0x44 0x44
- 0x2E, 0xD2
- t1-t2-t3
HX-RIO3 Series