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WD: Watchdog timer

FAST Serial Protocol: Overview & First Steps

This documentation section is about the FAST Serial Protocol (FSP) commands, which are the low-level commands a host computer sends to a FAST board. Most FAST Pinball makers do not need to know about these details, since the pinball game framework (such as the Mission Pinball Framework) handles this communication for you.

If you're writing your own game framework, read the overview of how FSP works and how to connect first.

The Watchdog is a timer that is counted down in milliseconds. If the timer reaches 0 the hardware is disabled. A typical timeout period is 500ms but can be adjusted based on the designers particular needs, and the speed at which the host computer can reliably deliver commands to the FAST platform.

The watchdog timer controls the original blanking control line used in traditional pinball machines. If blanking is enabled, lamp matrix, display, and drivers are all disabled. All of the FAST platform boards have a visual LED indicator showing the blanking state. If that indicator is on, the hardware is blanking (disabled). If the indicator is off, the hardware is enabled.

Setting the Watchdog timer


  • <TIME> Time (in ms) until timeout

Return Values

  • WD:P Valid watchdog command submitted

  • WD:X Invalid watchdog command submitted

  • WD:F Invalid watchdog command submitted or CH: command has not been successfully sent yet.

Disabling the WatchDog Timer

You can disable the WatchDog timer functionality by setting it to 0.

WD:0<CR> (Returns WX:FFFFFFFF)

Reading the Watchdog Timer


Return Values

  • WD:<TIME>

  • WD: FFFFFFFF (if WD is off)

Note: The CH: command must be set prior and match the correct hardware platform or the watchdog will fail being set. This is to prevent running the wrong application on incorrect hardware. See the CH: command and iP: command for more information.

Documentation Feedback? Requests? Confused?

Hi! I'm Brian, and I'm responsible for the documentation at FAST Pinball. If you have any feedback, requests, corrections, ideas, or any other thoughts about this documentation, please let me know! You can email me at Thanks!

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