A rant about port configurations

[tekart]

Would it be quick (or even possible) to do a 'switch off everything' header?

Cool! I LIKE that. Darrell - does that sound feasible? Is it "just code"? I would totally value a header that disables ALL peripherals so I could knowingly start from a clean slate.

[Darrel Taylor]

That's the point!
Everything is already OFF.

Except the comparators on old chips, which can be turned off easily with ...
INCLUDE "AllDigital.pbp"
But that also enables all Digital Inputs, so technically everything's not OFF anymore.

Some REALLY OLD 12-bit chips made the T0CKI pin unable to control the TRIS bit while TMR0 was "OFF".
So that's about the extent of the "Turn it all off" header wizard.

; if chip has a 12-bit core
OPTION_REG.5 = 0 ; Free TRISIO.2 bit

But then again, you're really turning something ON (TMR0).

Don't worry about turning things OFF.
Turn stuff ON if you want to use it.

[tekart]

Thanks for that Darrell. Thing is I only need to learn a new PIC every 12-18 months, so I tend to forget how to set them up. I had really never seen it as "everything is already OFF". As I blunder around a new spec sheet I get distracted by all the registers and features and tend to lose sight of the basics.
Sometimes it takes someone like you to make the obvious clear. Like Charles, I tend to start off in shotgun mode and try setting all the registers. I see now that I have to think of the PIC as a blank slate (except for the comparators).

I guess I should re-word my rant to: "Why the heck do PIC chips all come with the blasted comparators enabled by default!" That has always tripped me up in the past. I don't see the reasoning behind it personally. Never used the comparator feature in all my years of PICing (15 and counting). But then I'm a simple soul...

[kenif]

Great timing as this exact problem has just consumed about 5 hours and I seem to hit a similar brick wall with every new PIC.

18F27J53 ~ outputs OK, inputs always read 0.
I know what the problem is, just can't fix it. Is there something else besides ADCON that needs setting?

Datasheet: ADON: A/D On bit 1 = A/D Converter module is enabled 0 = A/D Converter module is disabled
Tried ADCON0 = $0F, ADCON0 = %00000000 and all the individual bits such as ADCON0.0 = 0.

Instead of a rant at Microchip, this should be a programming project or feature request for the IDE.
Heck, if I knew how to set ADCON, I'd program it myself...

[HenrikOlsson]

Hi,
The ADCON register controls the the actual converter, not the input buffers of the pins. For the 27J53, check the ANCON0 and ANCON1 registers, page 371 in the datasheet.

The ANCON0 and ANCON1 registers are used to configure the operation of the I/O pin associated with each analog channel. Setting any one of the PCFG bits configures the corresponding pin to operate as a digital
only I/O. Clearing a bit configures the pin to operate as an analog input for either the A/D Converter or the comparator module. All digital peripherals are disabled and digital inputs read as ‘0’. As a rule, I/O pins that are multiplexed with analog inputs default to analog operation on device Resets.

Looking up ANCON0 and ANCON1 in table 5.1 (page 76) shows that they default to all zeros at POR meaning that when the chip powers up all analog pins are analog.

/Henrik.

[kenif]

Thanks, Henrik, that did it.
I'll be back on this project in a couple of days and you saved a lot of brain hurt.
Ken