Hi. I'm working on a spare-time project where I have to decode a PWM coded signal. The bit protocol looks like this: Frequency is 500Khz, each bit starts with a raising edge. One bits have a high duty cycle of 75%. Zero bits have a high duty cycle of 25% (with a bit of margin of cause). Now I want to read this stream into a microcontroller or DSP. I wonder what would be the simplest way to decode this signal and split it into a clock and data-stream (so I can read it in via SPI or so). Are there any ready made converter chips that receive PWM coded single wire protocols like the one I've just described and output something more standard like SPI or so? A built-in FIFO would also come very handy. Best, Nils

Sounds like you could decode it with a PLL locking on the rising edges, and sampling your signal at the (mid point) falling edge of the recovered clock. You also could use a 1us pulse from a mono-stable triggered on the rising edge, and sampling on the falling edge. The first is more tolerant of frequency wandering, but requires that data always be present. The second handles starting and stopping.

Single Chip PWM decoders?

Mar 02, 2014 22 Replies

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Arlet Ottens 12 years ago

Instead of letting the CPU read the values in a tight loop, some microcontrollers can use the DMA + Timer to automatically read a GPIO register into a memory buffer at accurately timed intervals. After reading a few hundred samples, the CPU can process the information in a burst, which should be more efficient than processing 1 bit/interrupt.

I've used this method in a recent project for 8 soft UART receivers, with little CPU overhead.

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Theo Markettos 12 years ago

Hmmm... I wonder if the DMA controller is Turing complete?

Theo

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David Brown 12 years ago

I don't think so, but it sometimes has a mind of its own...

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