please help with simple PICmicro 16F627a Oscillator Circuit

Hi, I have been trying to find some information how to use only a resistor and capacitor for my oscillator instead of a crystall or ceramic oscillator, I have read that this is possible to do if timimg is not critical. I am very new to micro's and have a working programmer/testboard but would like to make a very simple circuit (preferably with a solderless breadboard) to use my PICs for experimenting, instead of my programmer/testboard(I am getting board with just having leds flash on and off! when I push a button).

On page 96 (98/180) of the data sheet:

it states that in Register 14-,1 bit 4, 1-0 (FOSC) you can set the oscillator to be an RC oscillator

This is what I would like to do, if possible but I am not sure how to connect a resistor and capcitor by themselves let alone connect them to the PIC.

Also, another option in Register 14 is to use an internal oscillator,does this mean you could just connect your VCC, GND and I/O lines and no oscillator is needed? If so that would be even better.

Any help with this, or direction to where I can find more info would be great.

Mike Rothe (Sorry about the formatting, I think I need a new newsreader program)

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Well I have found out more about oscillators on the microchip site

Mike Rothe

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Well, take a look at page 99 of the data sheet, esp. picture 14-5

Thats right.

HTH Wolfgang

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I use the 16F627 in my electronic ignition module. Timing (such as measuring RPM and sending the spark out at the right timing angle) is what it is all about. I chose to implement the design with only using the internal 4Mhz clock. It appears to be quite accurate. I set the hex loader program PPP to set the right flags to use the internal clock.

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The internal clock is fine and very useful, once you determined the actual clock. The 627a has a calibration and usually falls within 10% of 4 MHz. The

627 (no 'a') though can be off a lot. I program about 10 of them a week and at least one of the bunch is runnig at around 3 MHz instead of 4! At least they do that pretty stable.

So if you want to do real world timing, you should check the internal frequency first and adjust the calculations in your firmware. My chips connect to an RS232 port, so I use the timing of the first byte sent to determine the chips internal clock rate and store it in the flash.

Oh, and one last thing. If you want to measure the internal clock speed, do

*not* connect a scope theo the oscillator out pin. The internal resistnce of the scope will throw the oscillator off! Write a program instead the toggle one of the port pins.