R9MWTU
5-2-55, Minamitsumori, Nishinari-ku, Osaka 557-0063 JAPAN
Phone: +81(6)6659-8201 Fax: +81(6)6659-8510 E-mail: [email protected]
EM-6221 Rev.9 P. 8 / 20
MODBUS - BASICS
This device conforms with Modbus-RTU protocol (MODBUS APPLICATION PROTOCOL V1.1a / Modbus over Serial Line
Specification & Implementation Guide V1.0).
The following communication parameters are selectable.
COMM. PROPERTY
SELECTION
Modbus address
1 to 99
Baud rate
4800 bps
9600 bps
19200 bps
38400 bps (*)
Parity bit
None
Odd (*)
Even
Stop bit
1 bit (*)
2 bits
Protocol
Modbus-RTU (Data length 8 bits) (*)
Modbus-ASCII (Data length 7 bits)
(*) Factory setting
When appropriately set, the host PC connected via RS-485 can read measurands from and write configurations (setting) to
the device.
All registers are assigned to Holding Registers, can be read out using Read Holding Registers or Read Input Registers com-
mand. If reading an address with no assigned register is attempted, ‘0’ is given.
Write Multiple Registers command is used to write registers. If writing an address with no assigned register is attempted,
‘Exception’ is given.
FUNCTION CODE
COMMAND
RECOMMENDED TIME OUT VALUE
03
Read Holding Registers
0.5 seconds
04
Read Input Registers
0.5 seconds
16
Write Multiple Registers
2 seconds
These commands enable reading measurands 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 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).
The 32-bit register 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 - OPERATIONS
■
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
