Hey guys,

Just wandering if you can suggest what is going wrong with my oscillator. I am using this: http://www.farnell.com/datasheets/64649.pdf

I have previously used the 4MHz oscillator for the clock input of the PIC16F84a, im now using the 20MHz model and is wired up the same, i.e. 1: n/c 7:gnd 8: output 14: +5v

I have attached a snap shot of the output, and as you can see its not the best

Thanks in advance

Attached Images

20MHz clock.jpg (43.5 KB, 15 views)

 

How did you check the oscillator with the test circuit given in the data sheet or from the PIC circuit?

Is your 4mhz is working correctly?
Best thing is to replace & see with another one.Are you sure that you working with a PIC16F84A not PIC16F84?

__________________
Gayan

My Website
http://gsmicro.blogspot.com/

 

Thanks for the quick reply,

I checked the oscillator on the PIC circuit, not using the test circuit in the data sheet. And the 4MHz is working great giving a good solid output.

I meant to say that i am using the 20MHz on the 16F74 and not the 16F84a, since the 16F74 requires a 20MHz clock source, but have wired it up the same. I have already swapped it over for a new one, which does exectly the same

Iv attached a quick drawing of how i have connected the Oscillator.

Thanks again

Attached Images

clock.JPG (11.1 KB, 14 views)

 

I mean a PIC16F84 not 74.Why the PIC output wont give any results?When using the 20MHz the PIC runs five times faster than 4MHz codings.
Are you sure with your codings?

__________________
Gayan

My Website
http://gsmicro.blogspot.com/

 

You don't show any decoupling capacitors?, presumably you have them?.

Also, why don't you just use a 20MHz crystal instead of a module?.

__________________
PIC programmer software, and PIC Tutorials at:
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Yes i do have a 0.1uF cap accross +vs and ground, forgot to add it onto the drawing

Im using the module because it is what i had available and have used before in other projects. Do you think the crystal would be better than the module?

Thanks

 

I suspect that you didn't select the HS oscillator in the config fuses!

 

You don't, you select external oscillator - although it's possible he's not selected that correctly?.

imhereithink: - try unplugging the PIC and scoping the oscillator, it may be that you have the fuses set wrong and it's loading the oscillator?.

__________________
PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

 

? You select the external oscillator in the High Speed mode: _HS_OSC if you use the config labels.

 

Standard crystal 20MHz is ideal for many Timing applications.I have being using for many circuits.also power consumption is mucher than a standard crystal in a mudule isn't it?

__________________
Gayan

My Website
http://gsmicro.blogspot.com/

 

Sorry, just checked the datasheet for the 16F74, and it doesn't have an 'external oscillator' option, like you said it says to set to HS.

__________________
PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

 

He is using the historic PIC16F84A.

__________________
Gayan

My Website
http://gsmicro.blogspot.com/

 

He's using the PIC16F84A-20, he must choose the HS osc.

 

Well he actually said:

__________________
PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

 

sorry for the confusion guys, i am currently using the 16F74. I was making reference to the 16F84a because i got the 4MHz oscillator to work on that.

Its the 20MHz oscillator on the 16F74 that i cannot get to work properly, here is the config_word i am using:

__config 0x3F10
;Configuration bits set as: Oscillator EXTERNAL 20MHz
; Watchdog Timer OFF
; Power-up Timer ON
; Code Protect OFF
Brown-out Detect OFF
; Master Clear Enable OFF
; Low Volatge Program OFF
; Data EE Read Protect OFF Code Protect OFF

Nigel i tried it without the PIC in place and still get the same reading