Editing Writing your first FV-1 program (section)

== Step 1: pass-through ==

The smallest useful program copies input to output.

<pre>
RDAX	ADCL, 1.0	; ACC = left input
WRAX	DACL, 0.0	; left output = ACC, then clear ACC

RDAX	ADCR, 1.0	; ACC = right input
WRAX	DACR, 0.0	; right output = ACC, then clear ACC
</pre>

Two instructions per channel.  <code>RDAX</code> reads a register into the accumulator, multiplying by the coefficient on the way in.  <code>WRAX</code> writes the accumulator to a register and then multiplies what remains in ACC by ''its'' coefficient.

That second coefficient is the part that catches people out.  <code>WRAX DACL, 0.0</code> means "write ACC to the left DAC, then zero the accumulator" — which is what you want before starting work on the other channel.  Using <code>WRAX DACL, 1.0</code> would leave the value in ACC and the right channel would come out as a mix of both.

Assemble this and play it through the simulator.  It should sound like nothing at all, which is the correct result.