Document the 2-wire mode as a A/B Quadrature output

[drf5n]

Per

Stepper/src/Stepper.h

Lines 36 to 39 in 4068b93

	* A slightly modified circuit around a Darlington transistor array or an
	* L293 H-bridge connects to only 2 microcontroller pins, inverts the signals
	* received, and delivers the 4 (2 plus 2 inverted ones) output signals
	* required for driving a stepper motor. Similarly the Arduino motor shield's

and

Stepper/src/Stepper.h

Lines 58 to 71 in 4068b93

	* Step C0 C1 C2 C3
	* 1 1 0 1 0
	* 2 0 1 1 0
	* 3 0 1 0 1
	* 4 1 0 0 1
	*
	* The sequence of control signals for 2 control wires is as follows
	* (columns C1 and C2 from above):
	*
	* Step C0 C1
	* 1 0 1
	* 2 1 1
	* 3 1 0
	* 4 0 0

Some modified H-bridge drivers and high-end configurable stepper drivers can use the 2-wire C0/C1 A/B Quadrature output from this constructor:

Stepper/src/Stepper.h

Line 86 in 4068b93

Stepper(int number_of_steps, int motor_pin_1, int motor_pin_2);

The TI L293x datasheet (pg 9) shows this circuit for how to wire it up with some inverters to use two signals to drive 2-phase quadrature input:

and

[drf5n]

Here's a Wokwi simulation showing how to use a STEP+DIR driver board with Stepper.h two-wire mode and how it needs 4x the steps to make a step:

https://wokwi.com/projects/360724869269076993