[Oberon] PO2013 - Real time measurement

[Paul Reed]

>  the PCB I have got also supports in-circuit serial
> programming through an adapter, that could also link to FPGA, possibly.

Certainly not the circuit you attached in your mail.  Take great care - 
I really wouldn't advise this kind of thing.  The FPGA will not play 
well with anything more than 3.3v levels.  I know.  :(

Since the PIC has such a wide operating voltage range, it is ideal for 
attaching to the FPGA without level conversion, sharing the same supply 
voltage.

People who mess with Raspberry Pis and Arduinos usually find out the 
difference between 5V logic and 3.3V logic the hard way.  Adding a 
traditional PIC programmer into the mix, with its 12-14V programming 
voltage on the same pin (MCLR) as has often a pullup resistor to Vdd (5V 
or 3.3V) is definitely asking for trouble.  Just saying...


> ...how it is synced when both
> SPI ends may run at different speeds. PIC16F818A runs at 8MHz, if I am
> correct.

I think you can run it up to 20MHz with an external oscillator but the 
datasheet isn't very clear to me on a first reading.  Anyway, the RISC 
processor and the PIC certainly wouldn't run synchronously in lock-step, 
instruction by instruction; they would run independently, communicating 
asynchronously, with SPI, for example, replacing the ad-hoc serial data 
link described in Prof. Wirth's "A Microcontroller System for 
Experimentation".

Cheers,
Paul