3.d. Jumpers

The qik jumpers allow you to easily alter the behavior of the device. These jumpers can be left off for most applications. If you use a jumper, it must be in place when the unit first starts up; changing the jumpers while the unit is running does not take effect until the qik is reset or power is cycled. The only exception to this is the removal of the demo mode jumper while the qik is in demo mode, which takes the qik out of demo mode.

Fixed-Baud Mode

The jumper labeled A on the bottom of the qik (i.e. the one closest to the edge of the board) sets the qik to fixed-baud mode when the shorting block is in place. When the shorting block is absent, the qik is auto-detect mode and determines the baud rate automatically when it receives the first 0xAA (170) byte. If you have a noisy serial connection or find that the automatic baud detection is not working well for your application, you can use a shorting block or some other jumper to ground pin A (the circular pin right next to the “A” silkscreen label). This fixes the qik’s baud rate at 38,400 bps, and the qik skips the automatic baud detection phase that normally occurs on start-up.

Enable-CRC Mode

The jumper labeled B on the bottom of the qik enables cyclic redundancy check (CRC) mode when the shorting block is in place. This allows you to increase the robustness of your qik connection through the addition of a CRC error-checking byte to the end of the command packets you send to the qik. The default behavior of the qik is to simply respond to a command packet once it receives the last byte. Grounding pin CRC (the circular pad right next to the “CRC” silkscreen label) causes the qik to expect an additional CRC byte at the end of every command packet. The CRC byte is the result of a CRC-7 computation on the entire command packet, as described in Section 6. If this byte does not match the expected CRC, the qik ignores the command and uses the ERR pin to announce a CRC error.

Demo Mode

If you short pin A to pin B (the circular pads right next to the silkscreen labels) and reset the qik, it enters demo mode and remains in demo mode for as long as the short is maintained. Demo mode gives you an easy way to test your qik and troubleshoot your application for potential problems. In demo mode, the qik smoothly ramps motor M0 from stopped to full-speed forward to full-speed reverse to stopped again over a few seconds. It then does the same for motor M1. The red (error) LED is on while motor M0 is active and off while motor M1 is active. The green (status) LED is on while the active motor is driving forward and off while the active motor is driving in reverse.

Demo mode can help you determine before you’ve even written any code if you have an issue with your power supply, such as insufficient ability to supply the current your motors are drawing or interference from motor noise.

While in demo mode, any serial data that is received by the qik on the RX line is echoed on the TX line, giving you an easy way to test your serial connection.