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QL: Driver Test Mode

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, we have a series of programming guides. Also, be sure to read the overview of how FSP works and how to connect first.

The QL: mode lets you step through your drivers one-by-one while observing the FAST driver ID number. This test pulses the driver for 15 ms at 50% PWM duty cycle, so first ensure your drivers can handle that duration and power.

Nano Controllers use N instead

The FAST Nano Controller uses the letter N for switch & driver-related commands instead of L. So everything here applies to the Nano too, except the commands are -N: /N: SN: DN: QN:.

This is an interactive command designed to be used via a terminal emulator.

Command Syntax


To use this command, you do NOT type Enter after the colon. Just type QL: and then use the Q, W, or Space to control the tests. Hit Enter to exit the test mode.


  • Q = Decrease Driver Number
  • W = Increase Driver Number
  • Space = Pulse the same driver again.

You must enable the watchdog for this to work!

If you're trying this command and nothing seems to be happening, it's probably because the watchdog on the controller has timed out. (For safety reasons, controller will not allow drivers to function until a watchdog command is sent.)

Details are in the watchdog reference section. In the meantime, you can use a value like:


That will enable the drivers for about 90 minutes. Just send a WD:1 when you're done which will disable them (technically that sets the watchdog to 1ms.)

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