WTD: suggestion for sulking 16F877

Are you using the ACTUAL 877 or are you using an 877A part? If you are using an 'A' part try disabling the brown out detector.

Jim

i/o

starting up

I don't know this part but.... Are the outputs open collector? Do you need to enable internal pull-ups or provide external ones?

Are you sure it did start to run ? How ?

Jan-Erik.

Other than seeing the supplies are stable and the osc in and out are looking exactly like what I would expect I see nothing from the part. So, how could I tell whether it started to run or not?

As I said in my original post, the reset pin is pulled up, I've triple checked the configuration word and I've searched all the Microchip website for anything like this. There was one posting about all the pins being held low but that was for someone who had written PORTE and accidentally driven the part into master/slave mode and so couldn't get anything out of PORTD, which isn't happening with mine. And, yes it is a 16F877, not a 16F877A.

Thanks

starting up

I'd also disable the Brownout and the startup timer for initial test purposes. Just use a long time constant (say 2 seconds) on the MCLR reset pin. I've had a similar lock-up problem in the past. Found it was a slow +5V power supply ramp-up. regards john

Aren't the port pins configured as Inputs at Reset? If you see all 0V then you probably are writing to the port config register correctly at least (otherwise any pull-ups on inputs will give you logic 1).

#include __CONFIG(0x3F33); main() { TRISB = 0x00; TRISC = 0x00; TRISD = 0xe0; PORTB=0x55; PORTC=0x55; PORTD=0x55; while(TRUE) ; }

I have tried all the suggestions people have made thus far.

With this config word I've turned off the brownout, turned off the power up delay, wired the reset input low and only let it go high several seconds after power up, checked that the supply is clean and has decoupling caps right next to the part, checked the RC oscillator to see that it is running cleanly, have nothing else connected to the part...

And all the outputs sit there sulking at logic low. I'm using a resistor & led as a cheap logic probe and every one of the pins pulls that led down hard enough to turn it on just as brightly as tying the led to ground. Voltmeter gives same results, almost 0v.

Anyone else got an idea?

Thanks

then

I guess your C compiler sets the banksel? Have you tried a simple ASM program like that?

Regards, Bob Monsen

Well, thanks to everyone who has had a suggestion. But nothing has worked yet. Here is the program read back out of the part and disassembled, with my comments included. There are a few redundant bytes of code there but I haven't turned on the compiler optimization, no need to add any more risk optimizer bugs by trying to squeeze a few bytes out of a 15 byte program.

My guess is that the part is never beginning to run. But I've disabled all the "features" and I manually hold reset low for seconds before it is allowed to run. It is a 5 amp supply driving a 50 ma part, it has decoupling caps, voltage polarity is right, part is repeatedly accepted by the programming hardware and confirms the programming. But maybe something is latching up the part. Microchip website searching turns up nothing. I'm stumped.

Any other ideas to try? Thanks

;__CONFIG(0x3F33); /* disable low voltage prog, disable brown-out, disable pwr up delay */ ;/* manually hold MCLR low for seconds after power up and then manually pull high */

Perhaps the ADC is causing problems?

The data sheet says..

and..

The suggested code is...

BCF STATUS, RP0 ; BCF STATUS, RP1 ; Bank0

CLRF PORTA ; Initialize PORTA by ; clearing output ; data latches

BSF STATUS, RP0 ; Select Bank 1 MOVLW 0x06 ; Configure all pins

MOVWF ADCON1 ; as digital inputs

MOVLW 0xCF ; Value used to ; initialize data ; direction

MOVWF TRISA ; Set RA as inputs ; RA as outputs ; TRISAare always ; read as '0'.

Sorry I didn't spot you were using port C not port A.

I understand, not like I haven't overlooked something before :) I picked port C for the simplest test because it wasn't multiplexed with master/slave or analog or ...

Before I reduced the code down to three lines, I had configured port A as digital and output copies of the switch inputs there, so I thought I could see the switch operation directly. And even that was still leaving all the port bits sitting at zero volts.

Thanks for trying, any other ideas?

...

I once had something similar on another PIC but it went away on it's own! I was writing in assembler and as far as I can tell the only change I made would have (in effect) added a small delay between power up and configuring the ports. Can't see how that would explain anything (you would expect other people to report the same problem).

I worked through the code you posted and it looks OK. I rechecked your config bit settings against the data sheet and they also look OK. I also checked that a Brown Out Reset didn't have a seperate reset vector to the normal one (it doesn't).

Do you get the same results on more than one 16F877 or isn't it possible?

Is the PCB layout good? Good grounding? Decoupling? Otherwise I'm stumped too.