Modbus - Basics - M-system 53U Operating Manual

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 247
Baud rate 1200 bps
2400 bps
4800 bps
9600 bps
19200 bps
38400 bps (*)
Parity bit None
Odd (*)
Even
Stop bit 1 bit (*)
2 bits
T1.5 timer length 0 to 6.0, in 0.1 increments (Modbus protocol standard: 1.5)
T3.5 timer length 0 to 6.0, in 0.1 increments (Modbus protocol standard: 3.5)
(*) 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 Read Holding Registers, can be read out using this command. If reading an address with no as-
signed 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
03
16
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 order can be reversed by programming.
The 32-bit register must be read out and written in single command sequence.
CAUTION: DO NOT apply new setting via Modbus and the front control buttons at once.
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.
COMMAND
Read Holding Registers
Write Multiple Registers
5-2-55, Minamitsumori, Nishinari-ku, Osaka 557-0063 JAPAN
Phone: +81(6)6659-8201 Fax: +81(6)6659-8510 E-mail: info@m-system.co.jp
RECOMMENDED TIME OUT VALUE
0.5 seconds
2 seconds
EM-6485-B Rev.21 P. 10 / 52
53U