How to modify this code to simulate a binary encoder?
You may try to bit-bang the protocol using direct port access. This
is less convenient, but way faster than digitalWrite(). Below is an
example, untested program. I am assuming the pinout is


data = PB0 = digital 8
clock = PB1 = digital 9
pins PB2 – PB5 (10 – 13) are unused


Edit: This updated program uses the clock as an input, and the data
as an output. The previous version used both lines as outputs, which was
due to a misunderstanding of mine.

#include &lt;avr/io.h&gt;

int main(void)
{
    uint16_t data = 0x155;

    DDRB  |= _BV(PB0);
    PORTB |= _BV(PB0);
    TCCR1B = _BV(CS10);  // start timer 1 @ F_CPU
    loop_until_bit_is_clear(PINB, PB1);

    for (;;) {
        loop_until_bit_is_set(PINB, PB1);
        PORTB = data &amp; 1;
        data &gt;&gt;= 1;
        TCNT1 = -304;        // 20 us * 16 MHz - 16 cycles
        TIFR1 |= _BV(TOV1);  // clear overflow flag
        while (bit_is_set(PINB, PB1)) {
            if (bit_is_set(TIFR1, TOV1)) {  // timer overflowed
                PORTB = 1;  // data high
                data = 0x155;
                loop_until_bit_is_clear(PINB, PB1);
                break;
            }
        }
    }
}


This should be able to operate at frequencies up to about
200&nbsp;–&nbsp;250&nbsp;kHz. There is a delay of about 0.5&nbsp;µs
between the rising edges of the clock and the data been sent out, with a
jitter of 3&nbsp;clock cycles.

The data word is sent least significant bit first, contrary to what the
protocol diagram shows. However, if you send arbitrary data, this should
not be an issue.

Note that this is a pure avr-libc program, which does not use the
Arduino core. It uses polling to check the inputs and the timer. The
interrupts are never enabled.