ENABLE: Microcontroller timer input configured to capture and interrupt on both edges. Signals the microcontroller whether the H Bridges should be powered up or not. Microcontroller remains powered on low power mode when ENABLE is LO and will operate accordingly when ENABLE is HI.

STEP: Microcontroller timer input configured to capture and interrupt on rising edges. A transition from LO to HI tells the microcontroller to issue a new step. Transitions from HI to LO are ignored, although it is the user’s prerogative to code this so that both transitions generate a step.

DIR: Microcontroller timer input configured to capture and interrupt on both edges. Selects the bipolar motor direction of rotation. LO implies counter clockwise rotation, while HI selects clockwise rotation. This was arbitrarily chosen and can be changed according to preference.

STP_RST: Microcontroller timer input configured to capture and interrupt on both edges. Clears the internal indexer and disables the H Bridge. When STP_RST is made LO, the indexer look up table is returned to pointer 0 and the H Bridge is disabled. When STP_RST returns to HI, the H Bridges are enabled and motion starts from look-up table position 0.

USMx: Microcontroller timer input configured to capture and interrupt on both edges. Selects the 8 possible degrees of microstepping resolution. In this application note, half step, quad step, as well as 8, 16, 32, 64, 128 and 256 degrees of microstepping were coded.

WFSx: Microcontroller interrupt input (GPIO). Waveform Select bits. Select from the eight internal look up tables.