Modbus master function – Yokogawa Button Operated MV2000 User Manual
Page 163
7-10
M-4662
Modbus Master Function
Basic Operation
• The MV, operating as a master device, communicates with slave devices periodically
by sending commands at specified intervals.
• This function is independent of the Modbus client function operating over the Ethernet
interface.
• The supported functions are (1) reading data from the input registers and hold
registers on a slave device and (2) writing data into the hold registers on a slave
device.
Serial Communication Specifications (same as with the Modbus slave
function)
Communication available via ModbusRTU
Communication media:
RS-232, RS-422, or RS-485
Control system:
No flow control (none only)
Baud rate:
Select 1200, 2400, 4800, 9600, 19200, or 38400.
Start bit:
1 (fixed)
Data length:
8 (fixed)
Parity:
Select odd, even, or none
Stop bit:
1 (fixed)
Message termination determination:
Time equivalent to 48 bits
Modbus Master Specifications
Read cycle:
Select the cycle for reading data from other devices from the
following:
125 ms, 250 ms, 500 ms, 1 s, 2 s, 5 s, and 10 s
Timeout value:
Select the timeout value when there is no response from a
specified slave after sending a command from the MV.
125 ms, 250 ms, 500 ms, 1 s, 2 s, 5 s, 10 s, and 1 min
Retry count:
Select the retry count when there is no response from a
specified device for a command sent from the MV
OFF, 1, 2, 3, 4, 5, 10, and 20
Auto recovery cycle:
Select the cycle for automatically recovering from the
following:
OFF, 1, 2, 5, 10, 20, 30 min, and 1 h
Wait between commands: Select the wait time
*
to send the next command after receiving
a response to the previous command from the following:
OFF, 5, 10, 15, 45, and 100 ms
* When communicating using an RS-485 two-wire system,
the signals may collide, because the master and slave
device communication drivers switch in half-duplex mode.
If communication does not work properly, increase the wait
time.
Command type:
R, R-M, W, and W-M
Command setup:
Set up to 16 commands
Command items:
Read channel 201 to 440, C01 to C60
Write channel 001 to 048, 101 to 160 (varies depending on
the model)
Address:
1 to 247
Input registers: Same as the Modbus client function.
Hold register:
Same as the Modbus client function.
Access method:
Same as the Modbus client function.
Supported functions:
Same as the Modbus client function.
Data type:
Same as the Modbus client function.
7.3 Modbus Protocol Specifications