Yokogawa Data Acquisition with PID Control CX2000 - Manual (Page 108)

4-14
IM 04L31A01-17E
Broadcast Request
Broadcast request is a function used to write the same data collectively to the hold
registers of all the Modbus slave devices connected to the Modbus master device.
• Broadcast request is achieved by setting the slave address number of a command
message to “00.”
• The command message that specifies this address functions regardless of the slave
address.
• The broadcast request can be used only on function codes 6 (write to single hold
register) and 16 (write to multiple hold registers).
• The CX does not return a response.
Host computer
(master station)
1200 m max.
Transmit the data at once.
* There are no responses from the slave stations.
Number of slave stations that
can be connected is 31.
Function Code
Modbus master devices use function codes to make the Modbus slave devices execute
the commands. The Modbus slave function of the CX supports the following function
codes.
Code Command
3 Read the hold register (4xxxx)
4 Read the input register (3xxxx)
6 Write to single hold register (4xxxx)
8 Loopback test
(However, the CX only returns test code 0x00.)
16 Write to multiple hold registers (4xxxx)
• Writing is not performed on read-only registers and forbidden registers
• Broadcasting request is allowed on function codes 6 and 16.
Read Multiple Hold Registers (Function Code 3)/Read Multiple Input Registers
(Function Code 4)
Reads the specified number of points consecutively from the registers from the specified
register number. The maximum number of points that can be read at once is 125.
• Command message
Slave
address Function
code Register start
number
(High) Register start
number
(Low) Number of
registers
(High) Number of
registers
(Low) Error
check
4.5 Communications as a Modbus Slave