Power problems

[skimask]

Post some code!!!

[languer]

You should have the MCLR set per the 16F877A datasheet. Note that the 16F887 "has a noise filter in the MCLR Reset path. The filter will detect and ignore small pulses.". This along with the different clock circuits on the 887 makes enough of a difference.

A simple test code which works on both the 877A and 887, as previously suggested, will also provide some insight.

[menta]

languar I didn't get you point.

DEFINE OSC 8
a var byte
a=0
TRISB=$0
test:
SEROUT PORTB.0,4,[254,128,#a]
a=a+1
pause 1000
goto test

end

[languer]

What I am trying to say is that the 887 and 877A are not exactly identical. The MCLR input (something that can be associated with such problems) are quite different on both devices. My suggestion is to connect the MCLR to Vdd on the 877A using the R-C-R circuitry in the datacheet.

Also, the OSC input circuitry are not the same on both devices. Do both circuits you have (i.e. working 887 and non-working 877A) use the same external crystal circuit, or does the 887 uses the internal oscillator?

The code you have posted works on the 887, but not on the 877A? Is this correct?

[menta]

I tried to connect the MCLR stright to the +5V. Didnt help. Will try with RCR.
887 use internal OSC while the 877A use an external.
The code works perfect on both devices when using the USB programmer to power up the circuit.
When I use the 7805 to power the 877A, it fails. 887 is running with the same 7805 with no problems.
I see that the program run, I see it print something every 1 second, It start to print 1,2 and then it print junk every 1 sec. Thats why I think the LCD get some noise. I tried with R-C to the ground, but it doesn't help.

[gringobomba14]

With regard to this circuit, take the 2803 out of the circuit and try it. If it still doesn't work, it's not power related, then we can look at noise somewhere. Have you got a photo of this setup?

[Archangel]

Hi Menta,
You know, the schematic you posted has 1 rather serious omission, in that it is sending AC and not DC to the regulators. Did you install a bridge between the transformer and the regulators? Cause ME-THINKS AC ain't going to work.