Writing good/proper code

[Bill Legge]

Thanks for the advice to date.

I'm not clear what use should be made of the Watch Dog timer?

Assume that no activity after X Seconds means something is wrong and re-start? Or is there more to this?

On a new additional subject: ST input pins. Recently I wanted to use the hysterisis of the ST pins and did a test to check the thresholds.
Found that PORTB.0 (used as an interrupt INT0) was way off spec for the chip PIC18F8722:

Go off at 1.6 V
Go on at 2.7 V

The spec gives:
Go off at 1.5 to 1.3 V
Go on at 3.0 to 3.4 V

Test voltages supplied via a 10k pot and measured with a good meter - my new FLUKE! The differences are considerably outside spec. Anyone else had difficulties with the ST pins?

Regards Bill Legge

[Ingvar]

Hi Bill,

You got the WDT right.

I must say that i've gone through more than my share of Microchips datasheets and i can't remember ever seeing anything else than the usual 0,2-0,8Vdd spec for ST inputs. So if you're running your pic on 5v, anything less than 1v(0,2*Vdd) is guaranteed to be read as a 0(low) by the pic. Anything above 4v(0,8*Vdd) is guaranteed to be seen as 1(high). Everything in between is to be considered as unknown. This means that your trippoint should be found somewhere in this region. It does not say anything about the amount of hysteresis. I haven't checked this for many years but when i did i found that the trippoint was just below 0.5Vdd and the hysteresis was quite small (<100mv). My memory may be way off though.

So, if i need an input with a specified trippoint and a specified ammount of hysteresis i use a comparator(or op) with external resistors.

/Ingvar