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EM-6224 Rev.9 P. 8 / 21
MODBUS - OPERATIONS
All registers are assigned to Holding Registers, which can be read out with Read Holding Registers or Read Input Registers
command. If reading an address with no assigned register is attempted, ‘0’ is given.
Write Multiple Registers command is used to write in registers. If writing an address with no assigned register is attempted,
‘Exception’ is given.
FUNCTION
COMMAND
EXPLANATION
RECOMMENDED TIME OUT VALUE
03
Read Holding Registers
Used to read registers
0.5 seconds
04
Read Input Registers
Used to read registers
0.5 seconds
16
Write Multiple Registers
Used to write in registers
2 seconds
These commands enable reading measured values and writing configurations.
One (1) word registers are represented in 16-bit integers, while two (2) word registers are in 32-bit. All registers are in the
form of signed integer unless specifically given in the explanations.
The lower digit word in a 32-bit register is assigned to the lower address (n), while the upper digit word is assigned to the
higher address (n+1).
Address
n
n + 1
Contents
Lower digit word
Upper digit word
The 32-bit register (2 words) must be read out and written in single command sequence.
It is recommended to wait for a time period indicated under ‘recommended time out value’ in the above table to receive a
response for a command. If no response is received for these time periods, take appropriate error processing such as retrying.
■
MODBUS REGISTER ACCESS SETTING
ADDR.
WORD
PARAMETER
8977
2
Passcode entry for deactivating Modbus register write protection
Write a preset passcode in this register to deactivate the write protection via Modbus.
When the value set in this register matches the preset passcode, ‘1’ is set in the register address 8979 to en-
able writing in Modbus registers.
The value set in this register cannot be read out. It reads always ‘-1’ regardless of the set value.
When writing in the Modbus registers for setting change is complete, be sure to set a value (‘0’ is recom-
mended) other than the passcode to activate the write protection again.
8979
1
Modbus register access setting
0 : Write disable (*)
1 : Write enable
Other : Write disable
This setting is cleared when the power supply to the unit is removed. It always starts with ‘0’ (Write dis-
able) when the power supply is turned on. Set ‘1’ before writing in other registers.
Note that ‘1’ (Write enable) cannot be written in this register when the Modbus register write protection
passcode is preset and the write protection is enabled.
Be sure to write the correct passcode in the register address 8977 before changing the register setting from
‘0’ (Write disable) to ‘1’ (Write enable).
(*) Factory setting
