6.3 Modbus Communications
196 SIEPCYEUOQ2V01A Q2V Technical Manual
■ Loopback Test
The loopback test uses function code 08 (Hex.) and returns the command message as a response message. This
test checks communication between the master and slave. The test code and data can use desired values.
These are examples of messages given out when the loopback test is done with the drive of slave 1.
Figure 6.10 Message Example When Doing the Loopback Test
■ Writing to Multiple Holding Registers
You can write the data that you set to the number of holding registers set in function code 10 (hex). You must
configure the number of the holding registers and each 8 higher bits and 8 lower bits in order in the command
message for the write data. You can write to a maximum of 16 holding registers.
These are example messages when you use the PLC to set Forward run in the drive of slave 1 with a 60.00 Hz
frequency reference.
Figure 6.11 Message Example When Writing to Multiple Holding Registers
Note:
The number of bytes set in the command message set the data quantity × 2 during the command message. The response message uses
the same formula.
When you rewrite the parameter value with the write command through the H5-11 [Mbus ENTER Command
Mode] setting, you must use the Enter command to save and enable the contents of the changes.
■ Reading from More than One Holding Register/Reading the Indicated Register
The drive uses function code 5A (Hex.) to write to more than one register, then it reads the contents of four
holding registers at the same time.
The function for writing to more than one register is the same as the function for function code 10 (Hex.). You can
write to a maximum of 16 holding registers.
The four holding registers to be read from are specified in H5-25 to H5-28 [Mbus 5A RegX Selection].
This table shows example messages when you write to more than one holding register or when you read more
than one command register, this register data is used for the examples:
• The drive for slave 1 is set for Forward run with a frequency reference of 60.00 Hz.
• The setting in H5-25 to H5-28 and the data in the specified holding registers are as follows.
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