RB0 + Internal Pullup + Interrupt

[Freman]

Hi again.

I've got a slight issue with my task.

I need PortB to have internal pullups on because I'm enhancing an existing board design that relied on them, however - I have an issue with implementing interrupts because RB0 is now high all the time and I need it to be low, I can achieve this by using a pulldown on top of the pullup, but my board space is running low

Is there a way to set RB0 not to use it's internal pullup?

[Archangel]

Hi again.

I've got a slight issue with my task.

I need PortB to have internal pullups on because I'm enhancing an existing board design that relied on them, however - I have an issue with implementing interrupts because RB0 is now high all the time and I need it to be low, I can achieve this by using a pulldown on top of the pullup, but my board space is running low

Is there a way to set RB0 not to use it's internal pullup?

Hi Freman,
Please tell us which PIC you are using . . .and without knowing that or seeing your board I ask if you have room for one of those SIP resistor ladders for pullups ?

[Freman]

Sorry, it was stupid of me to forget the pic - it's a PIC16F628A

And no, I really have no room left for much more on that board, I can probably cram one more resistor in as a pulldown but that's about it.

[Archangel]

Sorry, it was stupid of me to forget the pic - it's a PIC16F628A

And no, I really have no room left for much more on that board, I can probably cram one more resistor in as a pulldown but that's about it.

Datasheet PP36 sec. 5.2 . . . "A single control bit can turn on ALL THE PULLUPS. . . . The weak pull up is automatically turned off when the port pin is configured as an output." I think you are stuck using the resistor unless you can flip the port's use in the software I E. instead of, if high then to if low then. I have a blinky running right now which toggles the tris on a port and as soon as it goes back to input the wpu is on.

[Freman]

I think I've found another side effect of using internal pullups...

I always figured if I couldn't get any other method working for this, I'd fallback to serial/uart communications...

I can't get the UART working

I'm using a usb>serial chip, but it's no real matter because both pins 7(RB1/RX) and 8(RB2/TX) are always high

Any ideas how I can get this working?

[Archangel]

I think I've found another side effect of using internal pullups...

I always figured if I couldn't get any other method working for this, I'd fallback to serial/uart communications...

I can't get the UART working

I'm using a usb>serial chip, but it's no real matter because both pins 7(RB1/RX) and 8(RB2/TX) are always high

Any ideas how I can get this working?

Hi Freeman,
Gotta see some code. USART Idles high, in normal operation.