Assume the stepper motor driver described in Exercise 8.14 is connected to a Gumnut core through a 6-bit output register at port address 8, with bits 0 to 5 of the register controlling signals in1, in2, en_a, in3, in4 and en_b, respectively. Write a Gumnut subroutine to step the motor one-quarter turn, either clockwise, if r2 is 0, or counterclockwise, if r2 is 1. Hint: The subroutine will need to keep track of the current state of the stepper motor control signals. Use a location in memory to save the state.
Exercise 8.14
The ST Microelectronics L298 IC is a dual full-bridge driver that can be used to drive the kind of stepper motor shown in Figure 8.12 on page 327. The connections between the L298 and the motor (in simplified form) are shown in Figure 8.44. Determine the sequences of values on the inputs to the L298 to drive the stepper motor clockwise and counterclockwise.
