PIC16F86A Hot

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jwhill2000

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..was wondering, I have worked with the PIC16F84 w/10MHz clock some and just tried out the 16F84A w/20MHz clock. I noticed that the 16F84A was really putting off some heat, almost too hot to touch. Is this normal? Thank.
 
Thanks for replies. Yes, it appears to me that the power connections between the two are identical - from the datasheets. My circuit is just a simple serial output to a terminal. I didn't change anything when I went from 84 to 84A, other than removing the 10MHz osc w/a 20MHz osc. The program worked fine, but the chip was hot.
 
It is normal for PIC's to generate some heat, but if what you are saying that the chip is almost unbearable to touch it may be shorted out internally. Is it in the same circuit/PCB?
 
Its on a breadboard. I'm new to this so it is very possible I have something wrong. But, it is odd that the 84 runs cool and the 84A hot. Could it have something to do with my unused I/O ports? What is the general rule? Should I make all unused port outputs and tie them hi? Should I enable pull-ups on all unused port-b ports?
 
Post a schematic, or at least a picture of the circuit on the breadboard. The PIC shouldn't get hot. Slightly warm is OK if it is driving a whole bunch of LEDs, etc.
As a general rule you should make the unused pins outputs or use pullups.
 

what is the full code on the PIC? try to restore 10MHz and check whether it is still hot?

Perhaps the chip you have used is PIC16F84A-04.
For a PIC16F84A-4 and Vdd between 4 to 5.5V upper frequency is just 4MHz
For a PIC16LF84A-4, above 3V power supply, the limit is 10MHz.
and For a PIC16F84A-20 for Vdd between 4..5 to 5.5 the limit is 20MHz.

Please what chip you might have used. even the software needs tuning for the serial terminal connection, perhaps.
 
Last edited:
If a PIC is getting too hot to touch, it's almost certainly been plugged in the wrong way round - PIC's generally run stone cold, although they may get slightly warm if they are supplying a lot of current.
 
Nigel Goodwin said:
If a PIC is getting too hot to touch, it's almost certainly been plugged in the wrong way round - PIC's generally run stone cold, although they may get slightly warm if they are supplying a lot of current.
Click to expand...

Possible Nigel. I was of the opinion that if a 16f84A-4 is worked with 20MHz oscillator, it might turn HOT.
 
mvs sarma said:
Possible Nigel. I was of the opinion that if a 16f84A-4 is worked with 20MHz oscillator, it might turn HOT.
Click to expand...

You are thinking there's a difference - personally I seriously doubt it, I've never seen (or heard of) a 4MHz PIC that won't work perfectly at 20MHz - I imagine they are exactly the same chip, off the same production line.
 
I run the 18F1320 at 40Mhz (10Mhz and 4x PLL) regularly and they get slightly warm but never hot.
 
I am in the process of reworking my breadboard and making it a bit neater. I'll let you know what I did or did not do wrong. Thanks.
 
jwhill2000 said:
I am in the process of reworking my breadboard and making it a bit neater. I'll let you know what I did or did not do wrong. Thanks.
Click to expand...

Like I said above, getting hot is a serious hardware fault - most commonly the chip the wrong way round, or perhaps (in your case on a breadboard) one pin out of line?.
 
The amount of time you spend preparing your breadboard setup is directly proportional to your ability to debug it if something goes wrong. Especially in this case a simple decent photograph of the board with the chip and the rest of the circuit would let us answer the question. I've reverse powered an AVR before much to the same effect. Good thing is it lived.
 
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