STM32 programming – Bit or Byte ‘Banging’ on AD9850

Bit or Byte banging, what is that exactly?!

Sometimes device(s) has no standard serial or parallel protocols as are I2C, SPI and others. Instead, just series of bits or bytes and separate clock. Excellent example is DDS chip AD9850 – we may chose or serial or parallel interfacing. On serial interfacing we using ‘bit banging’ – we put one bit on GPIO port, then on another GPIO port one clock, then next bit on port… until all bites are transferred. Then we send frequency and phase update on third wire, brief pulse 1 then 0. If we want parallel (8 times faster) interfacing, we put whole byte on 8 pins, in our example GPIO A0 to A7, then on another wire we ‘fire’ clock pulse, and after transferring all data, also ‘firing’ update frequency and phase.  Before proceed to our program in Keil, we should to consult our datasheet about AD9850:

FM radio or Frequency Wobbler

In the codes below, there are two options: FM radio (chose for example 1/3 of the frequency, say 33 MHz, then ‘catch’ third harmonic on 99 MHz, and use comparator for getting almost square wave, so that odd harmonics are stronger), or “Frequency Wobbler”, excellent tool for RLC circuit characterization (testing band pass, low pass, notch and other filters as well as resonant circuits) from 0 to 62.5 MHz with AD9850 – or up to 90 MHz with AD9851, which is really hard to find.  You may change code so that sweep is only upward, and then program one pin before sweep to output short pulse for oscilloscope external trigger. Or leave as is and listen on SDR Software Defined Radio response from RLC circuits.

I made both options available in the same program, just pay attention to GPIOA registers – there are difference in the case of serial and in the case of parallel interfacing. Also, for serial or parallel, there are functions “dds_update_freqS” and “dds_update_freqP”, probably you correctly guessed, ‘P’ is for parallel, ‘S’ is for serial. Now, copy paste this code as usually onto your Keil editor:

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