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emir506
Joined: 23 Dec 2011
Posts: 2
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| 18f452 and 16f877 strange problem |
 Posted: Fri Dec 23, 2011 4:32 am |
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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 ?
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temtronic
Joined: 01 Jul 2010
Posts: 9221
Location: Greensville,Ontario
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| Posted: Fri Dec 23, 2011 6:35 am |
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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. |
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emir506
Joined: 23 Dec 2011
Posts: 2
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| Posted: Fri Dec 23, 2011 7:11 am |
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| temtronic wrote: | 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. |
Thank you for reply.
The pinout is exactly the same.
The schematic of PCB1 and PCB2 is the same, but the layout is different.
And for the moments I saw some output on LCD also for the not working PIC 18f452, but it was just for the short time, and the displayed text wasn't displayed correctly...
I dont have the first PCB anymore. So I bought new MC today, to test if the chip is dead. Will do the test later and come with results.
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There is always something |
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Ttelmah
Joined: 11 Mar 2010
Posts: 19499
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| Posted: Fri Dec 23, 2011 9:00 am |
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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 |
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