PIC16F877A not working again :(

[The Master]

Hi, Ive not touched 16F877A's for a while but now i need to use one again and im having more problems with it. Ive written some test code and ive tried mister_e's code from last time. My test code uses portD but ive tested ports A and B with mister_e's code too and im not picking anything up. Ive done all the usual checks (MCLR, Resonator, Capacitor etc). Ive checked the voltage with my oscilloscope and its extremely smooth. It almost looks like theres no load on it at all. The PIC is definately connected to it so im guessing its just not starting up correctly.

Im sure i got it working last time but i dont know how and im out of ideas now. I dont have any beer this time either . Does anyone have any ideas?

[skimask]

Hi, Ive not touched 16F877A's for a while but now i need to use one again and im having more problems with it. Ive written some test code and ive tried mister_e's code from last time. My test code uses portD but ive tested ports A and B with mister_e's code too and im not picking anything up. Ive done all the usual checks (MCLR, Resonator, Capacitor etc). Ive checked the voltage with my oscilloscope and its extremely smooth. It almost looks like theres no load on it at all. The PIC is definately connected to it so im guessing its just not starting up correctly.

Sir...SIR!!!!
Put down the PIC...now step away from the PIC...Hands behind your ankles...
Is it in backwards? Ya never, know...could happen...
And this is my favorite test code...absolutely nothing fancy, but it tells me that things are working...

temp var byte
trisa = 0  'set all the pins to outputs
trisb = 0
trisc = 0
trisd = 0
trise = 0
'also turn analog ports to digital and/or set cmcon if applicable
main:
temp = temp + 1
porta=temp
portb=temp
portc=temp
portd = temp
porte = temp
'put a pauseus xxx here if the fastest pin (bit 0 for each port) is entirely too fast
goto main

That way each successive pin on each port will have exactly half the frequency of the pin before it. Of course things change with each different type of PIC and it's application, i.e. whether or not I'm using MCLR as MCLR or an I/O, whether or not I'm using OSC1/OSC2 as clock pins or I/O, and so on and so on...

[The Master]

Its not in backwards. I know it can happen, Ive done it pleanty of times myself. Usually i put it in the programmer the wrong way. This is definately correct though. I am using the OSC1 and OSC2 pins for a 3 pin resonator (20MHz). MCLR is being used as MCLR. I dont see any options to use it as an I/O pin on this chip. It has a 10K resistor to VDD.

CMCON doesnt make much sense to me but that only seems to affect portA. My Code tested portD by turning 2 outputs on and off alternately. mister_e's code tests both portA and portB. I had trouble with portA before but at least portB worked. The only thing i see about portD is that it can act as a parallel port. The datasheet says trisE.4 must be set to enable "PSPMODE" but its default value is 0 so portD should be working as normal I/O pins.

The values of portD are unknown at startup. Usually that means the LEDs i have connected will flash sometimes when the PIC powers up. This time there not doing. Its like the chip is never turning on. I thought there might be a problem with my breadboard so i tested the power pins on the PIC and there is definately power getting there.

Ill have a go with your test code when i get home but for now ill continue reading the datasheet to see if there are any other registers that might affect it

[Acetronics2]

Ha,Ha,Ha

ive tried mister_e's code from last time.

 ifdef PM_USED
            device  pic16F877A, xt_osc, wdt_on, lvp_off, protect_off
        else
            __config _XT_OSC & _WDT_ON & _LVP_OFF & _CP_OFF
        endif
        endasm

I am using the OSC1 and OSC2 pins for a 3 pin resonator (20MHz).

Dit you also try to heat your pic, just some degrees ????

could be another solution ... the Hardware one

Alain

[The Master]

I know last time i was using a 4MHz one instead. Whats bad about using that code with a 20MHz?

The test code i wrote myself has "DEFINE OSC 20" at the top so that should have worked

Edit: The PIC didnt get noticably warmer at all

[skimask]

I know last time i was using a 4MHz one instead. Whats bad about using that code with a 20MHz?
The test code i wrote myself has "DEFINE OSC 20" at the top so that should have worked
Edit: The PIC didnt get noticably warmer at all

Check the datasheet, Oscillator section in particular...
Have to change the oscillator configuration from XT to HS when using a higher frequency crystal/resonator/etc.

[The Master]

Ive got another slight problem with this. Ive just tried to control some optoisolators using porte.0 and porte.2. For some strange reason the pins just wont turn on. I added some test code and the correct data is getting to the chip. It copies a bit from the serial data directly to the pin (EG, porte.0=btemp.0). Right after if i check the status of the pin it shows as 0. Ive had a look in the datasheet and i can see that porte gets used for parallel communications but i have set the tris registers to disable it and use it as a general I/O. I have something else connected to porte.1 and that works fine :S

Edit: It seems that changing the status of another pin is causing those pins to turn off. I had this the other night with portA too. Turning 1 output on would turn another off automatically. Im going to look through all the code again incase theres a silly mistake somewhere

[mackrackit]

What are you doing with the analog settings or pins.?

[The Master]

Im not using any analogue. The datasheet says analogue is disabled if ADCON1.0 is 0. It also says that its 0 by default.

I seem to remember these outputs working before by they arnt doing now. Ive not added any code that changes the state of those pins anywhere except the 1 line

[mackrackit]

Try adding this to the start of your code.

ADCON1=7 
CMCON=7

[The Master]

That worked Now ive just gotta read the datasheet and find out why

Thanx