RG-MHMOD 8
Drive Setup & Operation
4.5 Unlocking & Locking Programming Parameters only
Registers #49 and #1 are used in Unlocking and Locking Programming Parameters.
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Writing to any writeable register other than #1 can be enabled by writing the Drive’s Programming
Password to Register #49 (Unlock Parameters). This would be done when Drive Control (start, forward/
reverse, keypad speed control, etc.) is not required.
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The Factory Default password is 19.
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Once Register #49 (Unlock Parameters) has been written, the writing of parameter registers is enabled
until Bit 1 of Register #1 has been set.
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 to communicate at least once every 5 seconds. As an example, Register #24 can be read
repeatedly for this purpose.
The action of a Watchdog timeout depends on the setting of the CONTROL parameter. If the CONTROL
parameter is set for:
− NORMAL or NORM NO HAND: Watchdog timeout takes the drive out of SERIAL control mode and
continues with normal operation.
− SERIAL SPEED or S SPD / NO HAND: Watchdog timeout takes the drive out of SERIAL control mode and
follows the action of the SERIAL LOSS parameter (Parameter 56).
− SERIAL AUTO or S AUTO / NO HND: In AUTO mode, these settings force the user to START the drive
through the serial link. It is fairly safe to assume that the user would intend to STOP the drive through the
serial link as well. Under these circumstances, a loss of serial communications is considered somewhat
more serious. Therefore, when a watchdog timeout occurs, the drive is taken out of SERIAL control
mode and tripped into a FLWR/SER FAULT regardless of the setting of the SERIAL LOSS parameter.
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. 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.
