[Oberon] PO2013 - Real time measurement

[Paul Reed]

> I found this programmer on the net, that I wish to give a try.
> Single sided PCB, soldering iron, that seems within reach of my hobby
> capabilities. Later as my knowledge and confidence grows, I may
> try programming through FPGA and PICL directly.

Seems like a lot of work when you have the FPGA solution already in 
PICL.Mod.  Compare the code to the programming commands in 
http://ww1.microchip.com/downloads/en/DeviceDoc/39603c.pdf.

Also, you probably don't want that programmer circuit, I think it's 
designed to run off the old +-12V RS232 voltages.  Old PIC programmers 
like that don't tend to work nowadays, since even if you have a USB to 
RS232 converter or an old laptop serial port, it probably won't generate 
the full voltage swings.  Google further if you don't believe me. :)

If the purpose of the exercise is to learn, I think building an analogue 
PIC programmer (with the high voltage programming pin) is a bit of a 
side-track.


> What I need to find out yet, how to best match the PIC  to FPGA
> frequency. PIC has got its own xtal, and may support also low cost RC
> resonator.

The PIC would run independently of the FPGA on its own oscillator, 
communicating by providing data on the SPI port when requested (ie as a 
slave).  That *is* a good use of interrupts (in the PIC).


> I was also thinking to use PIC as a single loop PID controller,
> Oberon then as a sort of supervision and visual layer for trends and
> some optimisations. Not sure though, we could do PID without FPU math,
> just using integers?

Interesting.  Googling, some PIC chips have a PID controller in 
hardware, it seems: 
http://ww1.microchip.com/downloads/en/AppNotes/90003136A.pdf

That note concludes that using the PIC16F161X's Proportional Integral 
Derivative (PID) peripheral takes 9 instruction cycles, whereas a 
software implementation would take about 1000.  I agree it might be a 
stretch to do full PID on an 8-bit PIC in software, but you never know - 
maybe fixed point in two bytes.  I know people who are a lot more 
experienced with PID than me, so I'll stop speculating now. :)

Cheers,
Paul