problem RB4-7 on a 18F876A

[mister_e]

The problem is certainely the internal pull-ups. too weak to be good. try lower value let's say 1K.

BTW it's always agood practice to pca something betwen a PIC and the exterior world if you plan to use long distance cables. Opto coupler are still a good choice.

RB6:rB7 are still programming pins... look at the programming sequence of your pic... it make me think it could be something around it or not.

How about your MCLR pin?

How about the whole setup.

Bad ground screening, bad proto-board may give you some serious headache... worst @20MHZ. You may try to remove (for testing purpose only) those capacitor around your crystal.

[sougata]

Hi,

Internal pull ups are weak as stated and Steve is again damn right. Optocontrollers do help but then you need an additional power line light the LEDs. PCB layout is equally important. If you post your whole code then we can find out if it is an interrupt issue. Normally a PIC would reset if it freezes, (WDT) so an improper code may put your PIC in endless loop especially interrupts. If you do not have an ICD then it is possible to dump some values of the SFRs related to PIC power, stack etc,. This would ease diagonisis what went wrong and where.

[mischl]

hello steve and sougata

thanks for your hints.

i plan to change this three inputs (b5,b6,b7) to change to a2,a3,a5 and renew to code from the interrupt handler to a subroutine.
on the build in board which makes some troubles, the long connection is on b5. b6 and b7 are in the device so about 10cm long.
i will make a separate regulator from 12v to 5v from the same power supply to source a relais. sink them with the long cable outside to ground. this ground is also the internal gnd from the circuit. did you think this is a problem? the relais contact then switch in the device the input a5.

the mclr pin is set with 1k to 5v.

the setup is on a proto-board...

in the actual test circuit i also add a debug_off, with no success.
interesting is that when the pic seems frozen and i read back the codes with melabs serial programmer, the code starts again normal when it is finished...

cheers

[sougata]

Hi,

If you change from PORTB to PORTA you will be loosing interrupts. So might limit the functionality of your system. Why not revise the pull-ups have a clean PS proper freewheeling diodes for the relays and so on

[mischl]

Why not revise the pull-ups have a clean PS proper freewheeling diodes for the relays and so on

what means this? external pull ups and then ... power supply something...?

sorry, my english is not so fine ;-)