16F877A help

[TKS]

hi all,

i have just terminated my program...

and have soldered my first test board...

but when i put in the PIC i think the OSC of 20Mhz doesn't do his job how could i test that..??

is there a way to test a OSC whit a multimeter..??

i only wanna do a basic test..??

do they fail often..?? can they resist any heat (soldering..)

i dunno what i did wrong..??

i used caps on it whit the value 33pF

TKS

are there more things i need to watch @..?? example the orientation of hte caps (+ or - ) and what about the OSC..????

 

[Exo]

Make sure you used the HS oscillator option...
20Mhz doesn't work with XT

 

[TKS]

yes...

i'm using HS option and in the datasheets ihav read that the 33pF should work..

how do i now if i need the rs res to put on it..??

and wich value does i need..?? 3 ohm>>??

TKS

 

[TKS]

can you measure

the quality of a cap when it s already soldered..??

maybe to much heat..???

TKS

the cpu works..that will say i can program and verify it succesfull..

i also hace the mclr @ 5volts..


TKS

but a simple doesn't want to flicker..

 

[TKS]

mmmOSC

on my osc is printed

"Orion 20.000"

is that famous..??


TKS

 

[TKS]

...

Sorry for my many posts..

but i have got a new idea..

if i put a 16F84a in my socket and put in in a mode that one pin of it gets his internal osc freq..

then i could fuse theother in that way that it graps that signal right..??

TKS

 

[Nigel Goodwin]

Re: yes...

i'm using HS option and in the datasheets ihav read that the 33pF should work..

how do i now if i need the rs res to put on it..??

and wich value does i need..?? 3 ohm>>??

TKS

It's very rare to need the resistor, the reason for it is to prevent the crystal been over driven - some crystals might need it, but it shouldn't prevent it oscillating at all.

First off you need to make sure it's all connected up correctly, in particular make sure that all Vcc and Vdd connections are made - you have to use them all!.

If you have access to a scope, check if it's oscillating - you MUST use a x10 probe, a x1 will stop the oscillator.

If you have no hardware problems, and presumably the PIC verified OK after programming?, you may have a software problem.

 

[TKS]

...

don't have a scope...


houston we have a problem..

does de osc has polarization like a led..????

and they fail often after soldering..??

and the caps what about them..??

TKS

will try to go to another store and buy the same again..

 

[Nigel Goodwin]

Re: ...

don't have a scope...


houston we have a problem..

does de osc has polarization like a led..????

and they fail often after soldering..??

and the caps what about them..??

No, crystals aren't polarised, like anything they can be damaged by excessive heat, but with any slight soldering ability at all it wouldn't be a problem.

 

[Matt(Pic progger)]

:idea:

Put this code into your chip, make sure that port c (or whatever you choose) has bit 0 as an output and bit 1 as an input e.g.


MOVLW B'11111110' ;MASK TO MAKE BIT 0 OUTPUT, REST INPUT
TRIS PORTC ;TRISTATE PORT C


TEST
BSF PORTC,0 ;TURN ON PORTC,0 THIS IS AN LED OUTPUT
BTFSS PORTC,1 ;IS PORT C HELD HIGH?
BCF PORTC,0 ;NO, TURN OFF PORTC,0 THIS IS AN LED OUTPUT
GOTO TEST ;LOOP FOREVER

Ok, IF the pic is running then when PORTC,1 is high (5V) the led will light, when it is low, it will go out...... You may have to change the ports and I/0 lines to suit your design.

Let us know how you get on!

 

[TKS]

mhhh

i think it is dead i'm now at work will tst is a.s.a.p..

what about the configs i use HS (20Mhz cristal..)
33pf

TKS

 

[Matt(Pic progger)]

:?
hmmm, not sure, I would have used 15pf as a first choice, 33 seems a bit high...... could be wrong tho :wink:

 

[TKS]

mhh..

ok well i read in the datasheets that 33 should work

(is the upper limit)


but i will buy some of 15pf...and try it whit them.

is it true that because of higher pf the osc function takes longer to stabilize..and that needs a higher delay time set in the pic..????

TKS

 

[Nigel Goodwin]

Re: mhh..

is it true that because of higher pf the osc function takes longer to stabilize..and that needs a higher delay time set in the pic..????

No, it might perhaps take a few more cycles to settle down, but it won't prevent it running.