problem with 16f877a

[jeanninemtv]

hi mates

i have problems with this chip, i program a 877 and it works, then i change the headers and add the lines for sut down the analog comparators, and it works on sim. but when i burn pic 877a  it works crazy...

have you expèrienced this kind of trouble?

[Ahmad_k]

Upload your code to see if there is a problem. But the program should work perfectly if you disable the analog comparator

[Parmin]

Hi jeanine

once I get a batch of bad crystal and all my program goes funny.

What symptom you see? what do you mean by works crazy?

Par.

[Rego]

i once have a burner that works on 16f877a and make a strange things on 877a...

which burner u use ?
an upload ur code for testing....

[jeanninemtv]

i am using jdm programmer, following all the indications... and pgm to ground while programming..

but i dont know why , for example, lcd works strange ... but if i use the same code with 877 

' previously changing device and commenting cvcon   ....'
and works fine in 877

the matter is that i have four 877a in stock and with this problem

[frasenci]

 i program a 877 and it works, then i change the headers and add the lines for sut down the analog comparators, and it works on sim. but

You are doing 2 simultaneous edits a time.
Try one by one , i.e. , first only changing header and so.

Double check the definition files for each device , 877 and 877A in your programmer software,.... headers, I am willing to expect only a software error. ( fuses ? )

As far as I know , there is NO functional difference between this 2 devices but Enhanced Flash Memory ( hence the " A " )

What are tose "lines" you are adding ? what do they instruct ?
Maybe you should listen to Amhad_k/Rego and share the code....

Good luck !

Greetings
Francisco

[Vague]

Have you checked this data sheet which lists the differences between the chips.
http://ww1.microchip.com/downloads/en/DeviceDoc/39591a.pdf
The 877A seems to be more noise sensitive than the 877, so check your power supply decoupling and don't just leave unused inputs floating.
If you post your code we could all have a look at it.
Good luck

[Parmin]

the matter is that i have four 877a in stock and with this problem

If all four of them works funny, then it is time to check the peripheral devices like Voltage input, decoupling capacitor, dry joints, Oscillator frequency etc.

If you program works before, it should not have reason not to work again.
Most of the time it works bad is the peripheral are not working right.

Par.

[chyelim]

Hi, which language you are using to write your code. Check the schematic also, the fuses must check and see if it is HS, RC, XT or others ?? If you use crystal 20mhZ is must be HS. At last check the schematic for the CRYSTAL, crystal must put near with the OSC pin, if put the distance of the crystal is too far from the PIC then also will cause problem. So feel free to ask if it is still can't work. I've met before the faulty like that and these steps actually solve my problems and I hope will be help on your problems also !! Good Luck friend !!