Lenze MCH Series Drives Modbus Communications - Manual (Page 13)

9 RG-MHMOD
Drive Setup & Operation
− 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 unlocking 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.
4.7 Monitoring Only Operation
1. Power up drive with serial enabled.
2. Simply read AC Tech Register #24 (Modbus Register #25) or any other readable register.
3. No unlocking or watchdog issues apply for monitoring.
4.8 Normal Control Operation Sequence
1. Power up drive with serial enabled.
2. Unlock control by writing a zero to Register #48.
3. Control drive operation via various commands to Register #1 (Start, Stop, etc.).
4. If the Watchdog Timer is enabled, keep it from timing out by assure that repeated reads of drive
status (Register #24 – 6 registers) are performed at reasonable intervals (typically less than 5 seconds
between reads because the Watchdog typically faults at 10 seconds).
5. Lock Control when drive operations are complete by writing a 2 to Register #1
(assert bit 1 of Register 1).
6. Drive is now returned to AUTO mode (control from the drive keypad and/or terminal strip).