Brick Motion Controller Hardware Reference Manual
Watchdog Timer
Brick Motion Controller has an on-board watchdog timer. This subsystem provides a fail-safe shutdown to guard against software and hardware malfunction. To keep it from tripping the hardware circuit for the watchdog timer requires that two basic conditions be met. First, it must see a DC voltage greater than approximately 4.75V. If the supply voltage is below this value, the circuit’s relay will trip and the card will shut down, Brick Motion Controller uses its own DC to DC converter to create 5V and +/-15V from the user supplied 24VDC. This prevents corruption of registers due to insufficient voltage.
The second necessary condition is that the timer must see a square wave input (provided by the Turbo PMAC software) of a frequency greater than approximately 25 Hz. In the foreground, the servo-interrupt routine decrements a counter (as long as the counter is greater than zero), causing the least significant bit of the timer to toggle. This bit is fed to the timer itself. At the end of each background cycle, the CPU resets the counter value to a maximum value set by variable I40 (or to 4096 if I40 is set to the default of 0). If the card, for whatever reason, due either to hardware or software problems, cannot set and clear this bit repeatedly at 25 Hz or greater, the timer will trip and the Turbo PMAC system will shut down.
Actions on Watchdog Timer Trip
When the timer trips due to either under-voltage or under-frequency, the system is latched into a reset state, with a red LED indicating watchdog failure. The processor stops operating and will not communicate. All Servo, MACRO, and I/O ICs are forced into their reset states, which force discrete outputs off, and proportional outputs (DAC, PWM, PFM) to zero-level. In Turbo PMAC2 systems there is a hard-contact relay with both normally open and normally closed contacts. In a system, these outputs should be used to drop power to the amplifiers and other key circuitry if the card fails. Once the watchdog timer has tripped, power to the Turbo PMAC must be cycled off and on, or the INIT/hardware reset line must be taken low, then high, to restore normal functioning.
Diagnosing Cause of Watchdog Timer Trip
Because the watchdog timer is designed to trip on a variety of hardware and software failures, and the trip makes it impossible to query the card, it can be difficult to determine the cause of the trip. The following procedure is recommended to figure out the cause:
1.Reset the Turbo PMAC normally, just power cycle the cycle power. If it does not trip again immediately, there is an intermittent software or hardware problem. Check for the following:
•Software events that overload the processor at times (e.g. additional servo-interrupt tasks, intensive
lookahead) or possible erroneous instruction (look for firmware or program checksum).
Review the Evaluating the Turbo PMAC’s Computational Load section of the Turbo USERS manual.
•5V power-supply disturbances
•Loose connections
2.If there is an immediate watchdog timer trip in Step 1, power up with the re-initialization switch pressed and hold in. If it does not trip now, there is a problem in the servo/phase task loading for the frequency, or an immediate software problem on the board. Check for the following:
•Phase and servo clock frequencies vs. the number of motors used by Turbo PMAC. These frequencies may need to be reduced.
•A PLC 0 or PLCC 0 program running immediately on power-up (I5 saved at 1 or 3) and taking too much time.
•User-written servo or phase program not returning properly.
3.If there is an immediate watchdog timer trip in Step 2, check for hardware issues:
