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F-5500 Thermal Mass Flow Meter Manual 06/17 - 2030 / 107023
Page 62
Model F-5500
OPERA
TION
i
Scope
This portion of the manual describes the Modbus implementation using RS485 serial
communication physical layer for the ONICON F-5500 Mass flow meter based on the
Modicon Modbus Protocol (PI-MBUS-300 Rev. J).
Modbus Protocol
MODBUS Protocol is an application layer messaging protocol that provides client/sever
communications between devices. MODBUS is a request/reply protocol and offers
services specified by function codes.
The size of the MODBUS Protocol Data Unit is limited by the size constraint inherited
from the first MODBUS implementation on Serial Line network (max. RS485
Application Data Unit = 256 bytes).
Therefore, MODBUS PDU for serial line communication = 256 – Server address (1
byte) – CRC (2 bytes) = 253 bytes.
RS485 ADU = 253 + Server address (1 byte) + CRC (2 bytes) = 256 bytes.
For more information on MODBUS go to the web site http://www.modbus.org/.
Command Request:
<Meter Address> <Function code> <Register start address high> <Register
start address low> <Register count high> <Register count low> <CRC high>
<CRC low>
Command Response:
<Meter Address> <Function code> <Data byte count> <Data register
high> <Data register low> ... <Data register high> <Data register low>
<CRC high> <CRC low>
NOTE: The data shown in brackets < > represents one byte of data.
Modbus Indicators
LED indicator LP3 cycles on and off to indicate that the F-5500 is operating.
LED indicator LP2 blinks when Modbus signals are received and LP1 blinks when
Modbus signals are transmitted.
F-5500 Commands Supported
The F-5500 supports the following commands:
1) Command 03: Read holding registers
2) Command 04: Read input register.
3) Command 06: Preset single register
Modbus Introduction
Modbus
Introduction
Modbus
Protocol
Modbus
Indicators
F-5500
Commands
Supported