
- Configuring the (bipolar) stepper

To make the setup easy, each of the two windings in the motor should
be grouped (measure the resistance between the wires on the stepper):
  Winding I  : pin STEP_A and pin STEP_B
  Winding II : pin STEP_C and pin STEP_D

The variable iac_step_seq is the stepping sequence, it works like this:
  Step 1, activate pin number iac_step_seq[1:0]
  Step 2, activate pin number iac_step_seq[3:2]
  Step 3, activate pin number iac_step_seq[5:4]
  Step 4, activate pin number iac_step_seq[7:6]

...where iac_step_seq[1:0] represents pin 00 (STEP_A) to pin 11 (STEP_D)

iac_step_seq must be set correctly else the stepper won't move.
Fortunately it is pretty easy, there are only 12 possible values of
the iac_step_seq as listed in the table below. Start with the first value
in the forwards coloumn and continue down the rows until the motor
works. If it rotates the wrong way, choose the value in the backwards
coloumn instead (same row).

Forwards - Backwards 
    0x1B - 0xE4
    0x1E - 0xE1
    0x27 - 0xD8
    0x2D - 0xD2
    0x26 - 0xC9
    0x29 - 0xC6
    0x4B - 0x86
    0x4E - 0x81
    0x43 - 0x8C
    0x4C - 0x83
    0x42 - 0x8D
    0x48 - 0x87



