Lenze MC Series Drives Modbus Communications - Manual (Page 12)

RG-MCMOD 8
Drive Setup & Operation
4.6 Watchdog Timer
All AC Tech drives are equipped with a Serial Link “Watchdog Timer”. If the Modbus Master wishes to
control the drive (start, stop, forward, reverse, etc.) it must first “Unlock Controls” (refer to section 5.10).
If the Watchdog Timer is enabled and controls have been unlocked, the Master MUST PERIODICALLY
COMMUNICATE with the drive or the timer will timeout. The timeout period is fixed at 10 seconds. It is
recommended that the drive be polled at least once every 5 seconds. Register #24 can be used for this
purpose.
The action of a Watchdog timeout depends on the setting of the CONTROL parameter. If the CONTROL
parameter is set for:
− LOCAL : the drive will stop when a serial timeout occurs.
− KEYPAD 2 (LOCAL contol without the need for TB-1 to run): the drive will stop when a serial timeout
occurs.
− REMOTE: serial timeout will not work since the drive cannot be unlocked in REMOTE mode.
− MC1000/3000 drives STOP when a serial timeout occurs. There is no fault for this. Any time CONTROL
is changed from LOCAL to REMOTE the drive STOPS immediately.
The Watchdog Timer does not operate unless Controls have been UNLOCKED via Register #48, or Parameter
writing has been unlocked via Register #49. In the case of unlocking parameters only, the watchdog timer
will disable write permissions but will otherwise continue with normal operation.
Watchdog Timer Controls
− For some applications, it is inappropriate to shut down the drive because of a Watchdog Timeout.
Therefore, we have provided a means of disabling the Watchdog using Programming Parameter
#57 (SERIAL LINK):
Programming Parameter #57 controls both the enabling of the serial link and the Watchdog. By
setting Parameter #57 to WITH TIMER enables the serial link WITH the Watchdog. Conversely,
setting Parameter #57 to WITHOUT TIMER enables the serial link WITHOUT the Watchdog.
− A Watchdog failure can be recognized by reading the drive status (AC Tech Registers #24 – 29) and
looking at the control mode. If it has reverted from SERIAL to LOCAL without the Modbus Master
commanding it via Register #1 bit 1 (LOCK) then a watchdog failure has occurred. Serial Control
can be reestablished by writing another unlock message to Register #48.
− If the Watchdog Timer has been disabled, the Unlock Control Register #48 or Unlock Writing
Register #49 must still be asserted in order to write to Register #1 (Drive Control) or to any of
the programming parameters (in case of unlocking writing). However, there are no longer any
constraints on how often the Master must communicate with the drive.