Yokogawa µR20000 - Manual (Page 36)

3-8
IM 04P01B01-17E
3.4 Modbus Slave Protocol Specifications
The Modbus slave protocol specifications of the recorder are as follows:
Serial Interface
Item Specifications
Transmission medium RS-422A/485
Flow control None only
Baud rate Select from 1200, 2400, 4800, 9600, 19200, or 38400 [bps]
Start bit Fixed to 1 bit
Stop bit Fixed to 1 bit
Parity check Select odd, even, or none (no parity).
Transmission mode RTU (Remote Terminal Unit) mode only
• Data length: 8 bits
• Data interval: 24 bits or less*
• Error detection: Uses CRC-16
* Determines message termination with a time interval to 3.5
characters or more.
Maximum number of
connected units
Four-wire system: 32 slave devices
Two-wire system: 31 slave devices
Slave Address
Address that can be set 1 to 32
Supported Functions
The function codes of the Modbus slave protocol that the recorder supports are shown
below. The recorder does not support broadcast commands.
Function Code Specifications Operation
3 Read the hold register (4xxxx). The master device reads the
communication input data
written using function codes 6
and 16.
4 Read the input register (3xxxx). The master device loads the
computed, measured, alarm,
and time data of the recordr.
6 Single write to hold register (4xxxx) The master device writes to
the communication input data
of the recorder.
8 Loopback test The master device performs a
loopback test of the recorder.
The recorder only supports
message return (test code
0x00*)
16 Write to the hold register (4xxxx) The master device writes to
the communication input data
of the recorder.
* Hexadecimal “00”
Communication Input Data
You can use the communication input data by describing it in the computing equations for
the computation channels.