18f452 and 16f877 strange problem

emir506 · Joined: 23 Dec 2011 Posts: 2

I made a PCB with Graphic LCD. I programmed two chips:
16f877 and 18f452 and both of them have worked perfectly.

I made a second PCB which is same as the first one.
I used the same already programed chips as above mentioned.
Now only 16f877 is working and 18f452 not.

Why ?
Rolling Eyes

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temtronic · Posted: Fri Dec 23, 2011 6:35 am

The fact that both PICs work in PCB #1 and not #2 , my guess is the 2nd PCB is NOT the same. Maybe a bad solder joint, whisker,open trace, etc.
Ring out with ohmeter,visually inspect with magnfying glass.
Compare every trace with the good board, flex the board.
You don't say what the pin assignments are but logically they cannot be the same, else both PICs would work.

emir506 · Joined: 23 Dec 2011 Posts: 2

Ttelmah · Joined: 11 Mar 2010 Posts: 19515

The only thing that is noticeably different about the 452, is that it is significantly more fussy about crystals. If a crystal has too much gain on a 677, it'll probably work. On the 452, it'll often oscillate at a wildly high frequency, and the chip not work. When the 452 came out I had to upgrade some existing board that use the older 16 chip, and had to add a series resistor to the crystal to get reliable operation.

Best Wishes