PORTC Weak Pull-ups on PIC16F1503

[Darrel Taylor]

Ok Alain,

If you can tell me what address that register is in, it will be added.

I'm betting you won't find that little bit of information.

[Darrel Taylor]

I guess Alain doesn't want to play.
Instead, he posted a bug report in the melabs forum without doing any research.

So Barry,
The 16F1503 doesn't have a WPUC register.

Yes, I know you'll find references to WPUC in the datasheet ... but it doesn't exist.
There is a WPUA, but no WPUC.

If you need pull-ups on PORTC, they'll have to be external.

[Aussie Barry]

Hi Darrel,

I did a bit of searching on this subject and found some conflicting information.
Microchip has released an errata document stating WPUC is not available for the PIC16F1503 but I also found another forum where a member had successfully implemented WPUC at H.'020E'
http://www.microchip.com.edgekey.net...051-print.aspx

I am not sure who to believe.
I really don't have room on my board for external pull-up resistors. I chose the PIC16F1503 because it was reported to have weak pull-ups on both PORTA and PORTC.
Is a workaround possible using H.'020E' address?

Cheers
Barry
VK2XBP

[Darrel Taylor]

The person that said he got PORTC pull-ups to work on a 16F1503, has a total of 1 post on that forum.
Completely unreliable source.

The register, and the pull-ups do not exist in hardware.
No amount of messing with the code will change that fact.

Attempting to write to that address will result in errors from the assembler.
You can use the FSR's to indirectly write to address 020E ... but no pull-ups will activate on PORTC, because they're not there.
And when you read it back it returns all 0's.
I have actually done that with a 16F1503.

I am not sure who to believe.

I'm Crushed!

[Aussie Barry]

Hi Darrel,

Thanks for the prompt reply and detailed explanation.
Please do not feel crushed. My comments were from complete despair and were not directed at you. I should have known better than to question your reply but I read that someone had managed to achieve what I wanted to do and I saw a glimmer of hope on the horizon.

Time for a re-think on how to achieve my desired result. Thankfully, I do like a good challenge

Cheers
Barry
VK2XBP

[Aussie Barry]

Perhaps I should look at using PIC16F1823 instead of the PIC16F1503?

Darrel, are you aware of any issues with WPUC on the PIC16F1823?

Cheers
Barry
VK2XBP

[Darrel Taylor]

On the 16F1823 ... the weak pull-ups on PORTC work fine.

[Acetronics2]

I guess Alain doesn't want to play.
Instead, he posted a bug report in the melabs forum without doing any research.

Apologies, Darrel ...

I 've forgotten to download their ....GRRRRR ... F... errata sheet !!!
errata happens so often it might automatically be included in the download ...

Alain

[Aussie Barry]

Hi All,

I have now swapped over to PIC16F1823 for this project and I am now having difficulty using pins on PORTA as inputs with Weak Pull-ups enabled.
I have stripped down my code as follows:

#CONFIG
        __config _CONFIG1, _FOSC_INTOSC & _WDTE_OFF & _MCLRE_OFF & _BOREN_OFF
        __config _CONFIG2, _PLLEN_OFF & _LVP_OFF & _WRT_HALF
#ENDCONFIG

OSCCON = %01101000              ; Fosc = 4MHz
                                ; Clock determined by Fosc<1:0> Config Word
DEFINE OSC 4                    ; Define oscillator as 4MHz

ANSELA = 0                      ; Set PORTA as digital I/O
ANSELC = 0                      ; Set PORTC as digital I/O
ADCON0.0 = 0                    ; Disable ADC
DACCON0.7 = 0                   ; Disable DAC
CM1CON0.7 = 0                   ; Disable comparator 1
CM2CON0.7 = 0                   ; Disable comparator 2
CPSCON0.7 = 0                   ; Disable CPS module
T1CON.7 = 0                     ; Timer1 OFF
TRISC = 0                       ; All PORTC as outputs
TRISA = 1                       ; All PORTA as inputa
OPTION_REG.7 = 0                ; Enable Weak Pull-ups
WPUA = %00111111                ; Pull-ups enabled on PORTA 


LED1 var PORTC.5
LED2 var PORTC.1

Start:                          ; Flash LED1 and LED2 at 1Hz


    high LED1
    High LED2
    Pause 500
    low LED1
    low LED2
    pause 500

     
Goto Start

The program flashes LED1 and LED2 as expected but I get strange readings when I probe PORTA.1, .2, .4 or .5 with my oscilloscope.
With PORTA set as digital inputs and weak pull-ups enables on PORTA I would expect those pins to read +5v but they are in fact reading 0v

I need to connect switches to PORTA.2, .4 and .5 to make selections for my program to function but can't switch these pins to ground if they are already permanently there!

Can anyone shed any light on what might be happening or what I might be doing wrong?

Cheers
Barry
VK2XBP

[Darrel Taylor]

Except for PORTA.0, you've set all PORTA pins to OUTPUT mode.

TRISA = 1                       ; All PORTA as inputa

By default at power-up, all pins are in INPUT mode.
So unless you need to set a pin to output, you don't need to change the TRIS register.

[Aussie Barry]

Oh Dear.....

I just want to crawl into a hole and hide form the world...

Thanks Darrel