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6
Useful Functions
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Chapter
6
03 (0x03) Read Holding Registers
The contents of slave holding registers are read.
Broadcast cannot be specified.
The start address of the holding register and the number of registers are specified.
Slave devices transmit data by converting the contents of each register to 2 bytes.
* Be sure to specify the setting code prior to reading setting values for each item.
* N = Number of registers
Example) Reading the contents from compensation (address 40057) to over (address 40058).
Note that the relative address is 0x38 when reading the compensation value.
The F701+ settings for this example are as follows.
* In function code 03, only the LO words or the HI words are read when the start address specifies
the LO words from a 32-bit integer data area, or the end of the start a number of registers
specifies HI words from a 32-bit integer data area.
[Request]
Function
1 byte
0x03
Start address
2 bytes
0x0000 to 0xFFFF
Number of registers
2 bytes
1 to 125 (0x7D)
[Response]
Function
1 byte
0x03
Data bytes
1 byte
2 x N *
Register value
N x 2 bytes
[Error response]
Error code
1 byte
0x83 (Fu0x80)
Exception code
1 byte
01 or 02 or 03
[Request]
Function
03
[Response]
Function
03
Start address (HI)
00
Data bytes
04
Start address (LO)
38
Compensation (HI)
00
Number of registers (HI)
00
Compensation (LO)
64
Number of registers (LO)
02
Over (HI)
00
Over (LO)
32
Compensation
100 (0x0064)
Over
50 (0x0032)
Summary of Contents for F701+
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