PIC 16F84A:Internal pull ups

[Electrix]

Hi, I am using the PIC 16F84A for my summer project. I am facing a problem. I have used the pull up enable feature in the 16F84 for PORT B pins, but upon simulation I notice that my PortB input pins are not on a High State. All the steps leading to the enabling have been done. In my circuit out of the 8 Port B pins, 4 are output and 4 are input. The datasheet says that when the PB pin is configured as an o/p pin, the pull up feature is disabled, since 4 of my PB pins are outputs, could this be the problem ??

Awaiting your views..

 

[Exo]

No, that won't be the problem. When some portB pins are inputs and others outputs, the input pins will still be PU'd.

It should work in simulation, it does here anyway. (MPLAB SIM that is)
Did you mind that the RBPU bit is negative logic? (bit clear = PU's on)

 

[Electrix]

Did you mind that the RBPU bit is negative logic? (bit clear = PU's on)

Yes I did that right. But it still wont work !! Another thing:AfterI turn the RBPU bit in the Option_Register, the next instruction in the simulator should show the corresp PB i/p pin in 1 state--is this correct ?

Are there any other changes needed to solve the problem ??

Awaiting your views.

 

[Exo]

Ah, made a mistake there , sorry...

MPLAB doesnt simulate the pullups, so you'll have to try it for real...

 

[Nigel Goodwin]

Ah, made a mistake there , sorry...

MPLAB doesnt simulate the pullups, so you'll have to try it for real...

Another reason for not using simulators! :lol:

 

[Exo]

Well, it depends.

The simulator has it quircks, but microchip keeps working on it, can't expect it to be 100% tops from the start.

On the other hand, there are many things you can only test and see happening in a simulator. Just because some things happen to fast to communicate to the outside fast enough to see.

It's not because something works it really happens as you think and want it to, so simulating is a big help.

In real complex project such as the satellite positioner i'm working on simulation had been a gift from heaven.