In SX Microcontrollers, SX/B Compiler and SX-Key Tool, Peter Van der Zee wrote:

Hi All;

If your purpose is to generate a PWM sourced analog output, then why not use the "pulse density" modulation approach. Unfortunately I do not know the name of this algorithm, but it only needs interrupts at the update rate, regardless of the value to be generated. On top of that the code is consistently just 6 instructions (always) and is bordering on trivial. No thinking to do whatsoever. Assembler of course, but trivial to create a function (or SX/B command for that matter).

The process is to continually add the desired DAC value to an accumulator, and set/clear the output bit depending on wheter the carry was set/cleared respectively:

DAC:   
                    mov     w,DACValue       (of course could be a constant)
                    add      DACAccum,w
                    sc
                    clrb      PortBit
                    snc
                    setb     PortBit

Simple as pie...... I use this a lot.

Cheers,

Peter (pjv)

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