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PIC Port Problems.....

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chevymn1964

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how to connect 74hc154 to another 74hc154

Hello, I was wondering if anyone has had the same problems that I have with a PIC16F84.... It seems like port decay! Im using a PIC16F84 that is controling a 74HC154 ( intput shift register ) and a 74HC595 ( output shift register ) and the problem that I am having is with the clock pin. It seems like it would clock 8 times to "shift" the data and after about 5 or 6 re progams to work out software bugs the i/o port would start to go away. I looked at it on the scope and when I would first start there would be a nice clean square wave and after a few re progams the low side of the edge's would start to round off instead of a "clean" on-off true square wave????? any ideas? can you only re program PIC19f84's a few times???? It makes troubleshooting my software very difficult!!! lol thank you!
 

namqn

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use a couple of 74hc154 in a circiut

It's difficult to tell what's going on if you don't show us how you connect your system.

I can confirm that a PIC16F84 can be reprogrammed a couple of thousands times.

Cheers,
 

spdchk

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connect 74hc154 to 74hc154

Be aware of ESD - Electro Static Discharge.
What you are mentioning is typically damage caused by (for example) Static electricity.
Make sure you ground both yourself and the programming unit before inserting
the PIC.
 

sento

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connect more chips for 74hc154

Pin 4 (MCLR) must be GROUNDED !!!
 

chevymn1964

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picport

Hummm I have to go check but I think I have pin4 going to Vcc? Pulling it low would reset it... Would that clrear my proplems?
 

BeeBop

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pic 19f84 programmer board

Hi,
Sento, WTF are you talking about?
Pin 4 (MCLR) must be GROUNDED !!!

That will keep the part in reset. It's /MCLR, so it must be pulled up to Vdd with a 1-10k resistor.

Ah, Chevyman, you just posted, you are correct, it needs to be tied high.

Do you have decoupling caps on your part?

Regards,
Robert
 

chevymn1964

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korean picport

lol BeeBop, Yeah I have a decoupling cap on each I.C. I ordered some more PIC's today... Its a strange problem I've got here.... Its driving me nuts with troubleshooting the software because as soon as I get it working the way I need it to work the dang clock port goes out..... lol..........
 

BeeBop

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pic port reset

Hey Chevyman,
You are referring to the clock pin you are using to drive your serial register chip, yes? How many chips are you driving? The max that any pin can source is 25 mA, which should be enough to just clock 2 chips, but... perhaps a buffer would help? Which pin on the PIC are you using?
Don't you just love PICing, at times like this? LOL
Best wishes,
Robert
 

chevymn1964

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Hey Robert,
Thanks for all of your help! I'm still really new to this programming so bear w/ me lol... I'm using a 19F84 and I am referring to the i/o port to drive the I.C.'s clock pins. I am only driving 2 I.C.'s..... I was using RB7 at first then it went bad so instead of buying a new PIC and a few hours of trouble-shooting I changed to RB2.... It worked for a while now it went south.... So, I'll try again on a other port. I might try a RA port this time.... well, at least until I get the new PIC's...... PIC's are great when they work!!! lol Take care -Ryan
 

BeeBop

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Hi Ryan,
So the pin no longer works? Have you tried using the old bin - the damaged one - with something else. I mean something simple like an LED just to see if the pin is permenantly damaged. Or for sure, the pin no longer works. It could be, as spdchk said, ESD. How do you program your chip, in circuit, or do you remove it and flash it in the programmer?
BTW, that is 16f, not 19f.
I hope you ordered some newer chips, rather than the f84. The 16F628A is about half the price of the 16F84A, and has twice the program memory, and about four times the RAM.
Anyway, keep us posted, and I'll keep a few brain cells focused on your problem.

Best wishes,
Robert
 

waseem

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Hi Ryan!
I have been working with PICs for the past three years and i have never faced such a problem. ESD may be the reason for your problems but these devices are properly protected against ESD.
My experience is that there is always a chance of a bug in the software.
It would be of great help if you can post your code, since it will help us to debug your code.
A check that you can do is to remove the other IC's from the board and then check with a scope wheather the clock is comming out or not.

Best Regards.
 

chevymn1964

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Hello all!
Well, I think I might have found the problem.... Two of the output pins on the output shift register were shorted... I don't know for sure if that was the problem but it fixed the problems that I was having lol maybe it was over-driving the i/o pin on the PIC??? I will let it run overnight and see if its still running in the morning and keep you all posted..... Thanks for all the great sugestions and help!!!!!
 

dodo_8008

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you have to connect it all time with +ve supply througth 10kohm resistor to prevent unexpected restart
 

yousafzai

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Take care of ur MCLR pin it sould be high all the time unless u want to reset ur micro.
 

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