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

Hi James;

The reason I modify the output port pins in the ISR is because I want to effect the required levels at EXACTLY the same instant, every time. If I did it in the mainline, then the timing of those port changes are subject to variations due to other things the mainline is doing. In other words, they are less deterministic.

So, if I pre-calculate what the next output levels are to be in the main line, and then output those at exactly the same spot in the next ISR, we get the transitions happening at exactly the same instant every time. Totally deterministic. When you look at it with a good scope, there is less than 2 nano seconds of jitter.

For precision pulses or frequencies this is required. Although I'm not sure if that level of accuracy is required by Bebop, it's easy to do, so why not?

In your case, if the bits are not set/cleared at the same instant, there could be problems in high speed UARTs.

If you post your total code with a description, I'd be happy to comment. If your code is long or secretive, perhaps you can pare it down, but of course please test the shortened version to confirm it still exhibits the identical problem.

Cheers,

Peter (pjv)

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