What is the main difference Bet. 16f877 vs 16f877A

[uludere72]

I couldn't see any differenece!!

[Melanie]

Go look again... how about Comparators and a Voltage Reference Module as a start...

[uludere72]

does it work properly with my ex program which is writen for 16f877 ..!!

[Melanie]

Do I have a crystal ball? Actually yes, there's one next to my monitor, but when I look in it I can see all kinds of things but unfortunately your program isn't one of them!

If you are blinking a LED on PortB, you got no worries...

If you are using any pin that is shared with a Comparator, then just like the Datasheet says... it's not going to work without adding code to disable those comparators first.

[uludere72]

thanks for your kind response
!

[Joann]

I also have the same problem,i have a code compiled for pic16f877
the data,clock pin is on porta pin,when i program it on pic16f877a i did not work.
how would i disable the comparator.

[sandeepdevang]

hi... i am working on a project called "sms based device control".... i am done with the circuit and have started working on the codes... i have written the codes keeping pic16f877a in mind... but the debugger available in the college is MPLAB ICD2.. which contains the pic16f877 IC.... is it possible for me to run the same pic16f877a code here... otherwise what do i do?

[ledsignmen]

I couldn't see any differenece!!

I have had code running in 16F877 for years. I have PortA.5 as input I have a 1K pullup on A.5. I have a push button that connects A.5 to ground when the button is pressed. I have set the lower 3 bits of CMCON = 1. I have set ADCON1 = 7. I have placed a .1 cap from pin 7 to ground. Any press of the button results in a RESET of the 16F877A.
There are no problems when I use 16F877 but the 16F877A resets ever time.
What do I try next ???

[mackrackit]

Try CMCON=7 instead of 1.

Do you have a pull-up of around 470 from MCLR to VDD?

[ledsignmen]

Dave,
Thanks for the input.
When I said that the lower 3 bits of CMCON were set = 1
I SHOULD have said that Each of the lower 3 bits is set to 1
which makes CMCON = %00000111 which = 7.

I do have a 1K pullup to +5 on MCLR.

I have also discovered that if I set the config bits for the 16F877A
to turn the Brownout reset = OFF the code I have been running in
the 16F877 now also runs perfectly in the 16F877A.

What is it about pulling PortA.7 to ground with a pushbutton switch that
could lead to a system reset ??? And why would turning the brownout
reset OFF correct that problem ???

Thanks,
Dan

[mackrackit]

Sounds like a power supply problem or maybe something causing a short when the button is pushed.

The data sheet states when VDD drops to 4V a you have a brown-out.
Are both VDDs powered? Check the voltage on VDD when the button is pushed.

Two points to clarify.
Why the .1 cap to ground and not a pull-up of say 10k?
PORTA.7??? pin 7 is PORTA.5.

[ledsignmen]

Dave,

Sorry about the mistakes in my typing . . .
I have TRIED a .1 cap to ground on PortA.5 because some comments in this thread indicated that might be of benefit. And it sort of makes sense as a method for smoothing out the switch bounce noise generated by a push button switch.

And there IS a 1K pullup on PortA.5.

It was my confusion that typed PortA.7 in the previous text.
I SHOULD have typed PortA.5 and got that mixed up with the pin number which resulted in my typing PortA.7.

This whole thing is about PortA.5 which is also Pin 7.

I do have +5 to both VDD pins and the 5 volt source is a 150 watt switching supply.

I have had a friend of mine look at VDD and Master Clear with his scope and both of these are steady as a rock when the push button is pressed and the whole thing RESETS.
Pressing the pushbutton to pull PortA.5 to ground does create a little noise from the switch bounce but I cannot see that any amount of noise on an input should result in a reset ??? Do you think ??

Thanks again,
Dan