B.6 Communications Timing
To prevent a communications overrun in the slave drive, the master should wait a certain time between sending messages to
the same drive. In the same way, the slave drive must wait before sending response messages to prevent an overrun in the
master. This section explains the message timing.
u
Command Messages from Master to Drive
The master must wait for a specified time between receiving a response and resending the same type of command to the same
slave drive to prevent overrun and data loss. The minimum wait time depends on the command as shown in the table below.
Table B.2 Minimum Wait Time for Sending Messages
Command Type Example Minimum Wait Time
1
• Control command (Run, Stop)
• Set inputs/outputs
• Read monitors and parameter values
5 ms
2 • Write parameters 50 ms
3 • Save changes using an Enter command
3 to 5 s
<1>
<1> If the drive receives command type 1 data during the minimum wait time, it will perform the command and then respond. However, if it receives
a command type 2 or 3 during that time, either a communication error will result or the command will be ignored.
Command message Response message Command message
PLC→Drive PLC→DriveDrive→PLC
24 bit length
Master Send
Wait Time
Time
Figure B.7 Minimum Wait Time for Sending Messages
u
Response Messages from Drive to Master
If the drive receives a command from the master, it will process the data received and wait for the time set in H5-06 until it
responds. Increase H5-06 if the drive response causes overrun in the master.
Time
Command message Response message Command message
PLC→Drive PLC→DriveDrive→PLC
24 bit length
H5-06
setting
Figure B.8 Minimum Response Wait Time
B.6 Communications Timing
YASKAWA ELECTRIC SIEP YEAHHP 01B YASKAWA AC Drive – A1000 HHP Programming Manual
323
B
MEMOBUS/Modbus
Communications
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