Watchdog

Programs the watchdog timer of the Q8 data acquisition system.

Library

qctools

Description

The Watchdog Module for the Q8 series of I/O cards provides a mechanism for using the watchdog timer on an installed Q8 I/O card. If the watchdog expires, then the analog outputs are reset to 0V and the digital outputs are reconfigured as digital inputs and pulled high. Hence, all digital outputs go high on watchdog expiration. The output of the block goes from zero to one at the next sampling instant. To stop the model on watchdog expiration, connect a Stop Simulation or Stop With Error block to the output of the Watchdog module.

Parameters and Dialog Box

Board Number

The board number of the I/O card. If there is only one Q8 board in your system, then the board number should be zero. The second Q8 board in your system is board number 1, etc.

Timeout Interval

The watchdog timer is a 32-bit counter. It supports any timeout period from 60 ns to 257.69803776 seconds (4.3 minutes) in 60 ns units. The period is generally programmed to be more than the sampling period of the model, but small enough that the model stops quickly after the watchdog expires. The output of the block changes at the next sampling instant after the watchdog timer expires.

The Watchdog Interrupt block may also be used to act on watchdog expiration. The Watchdog Interrupt block is an asynchronous block that is executed immediately upon expiration of the watchdog timer, independent of the sampling period of the model.

Sample Time

A sample time must be specified for all discrete blocks. The default value extracts the sample time from the RTW Options dialog, under Solver/Fixed step size. A numeric value rather than 'auto' should be specified in this dialog field for this default to make sense.

Enable WATCHDOG Output

Checking this option enables output of the watchdog state to the WATCHDOG pin on the CONTROL header of the Q8 terminal board. The output remains high as long as the watchdog timer has not expired. If the watchdog expires then the output goes low. This signal can be used to shut off external hardware, such as current amplifiers for robot motors.

It can also be fed to the EXT_INT pin of other Q8 cards (available on the CONTROL header of the Q8 terminal board) in order to propagate the watchdog functionality to the other cards. Use one of the External Interrupt, External Status or Poll External Interrupt blocks with the other cards and check the "EXT_INT acts as watchdog" option. When EXT_INT is configured as a watchdog, a falling-edge on the EXT_INT line causes all the analog outputs of the card to be reset to zero and all the digital I/O lines to be pulled high, just like a watchdog timer. The EXT_INT line can also be programmed to act upon a rising edge.