Arrangement For Interlock Among Target Devices; Maximum Communication Time Per Target Device Station - Mitsubishi Electric MELSEC iQ-R Series User Manual

18.2

Arrangement for Interlock among Target Devices

When using the multidrop connection to communicate data between target devices and the CPU module in a m:n basis, the
interlocks need to be configured among the target devices to prevent more than one target devices from communicating data
with the CPU module at the same time.
The arrangements necessary for providing the interlocks among the target devices in order for one of the target devices to
communicate data with the CPU module are as shown below.
(Arrangements for priority use of the line (obtaining line ownership) from the start to the end of data communications with the
CPU module.)

Maximum communication time per target device station

Determine the maximum time for each target device to communicate data with the CPU module once it obtained the line
ownership.
This prevents loss of data communications between other devices and the CPU module in such cases as the target device,
which obtained the line ownership, went down.
Ex.
Target device 1
Target device 2
Target device 5
Start of data communications
• The maximum data communication time per target device station must be the maximum time required by
the respective devices to communicate data with the CPU module.
• The device which obtained the line ownership must complete data communication with the CPU module
within the maximum data communication time after the system started. (If data communications cannot be
completed within the time, initialize the C24 transmission sequence by transmitting the EOT/CL code to the
target CPU module within the maximum communication time. ( MELSEC Communication Protocol
Reference Manual)
• While a target device and the CPU module are communicating data, have the other devices check for
timeout so that they do not transmit data during this time.
18 DATA COMMUNICATIONS BETWEEN TARGET DEVICE AND CPU MODULE IN M:N BASIS
368
18.2 Arrangement for Interlock among Target Devices
Time
: Indicates the range within which the target device
cannot obtain line ownership.
: Indicates the range within which the target device
can obtain line ownership and can have data
communication with the CPU module.