please help with simple PICmicro 16F627a Oscillator Circuit

M

Mike

Guest
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:

http://ww1.microchip.com/downloads/en/DeviceDoc/40044D.pdf

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





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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:

http://ww1.microchip.com/downloads/en/DeviceDoc/40044D.pdf

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

http://ww1.microchip.com/downloads/en/DeviceDoc/osilator.pdf

Mike Rothe


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Dear Mike,

Mike wrote:
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.
Click to expand...
Well, take a look at page 99 of the data sheet, esp. picture 14-5

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?
Click to expand...
Thats right.

HTH
Wolfgang

--
From-address is Spam trap
Use: wolfgang (dot) mahringer (at) sbg (dot) at
 
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.




"Mike" <mike@therothe.com> wrote in message
news:XMase.1708767$6l.109308@pd7tw2no...
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:

http://ww1.microchip.com/downloads/en/DeviceDoc/40044D.pdf

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)


--------------= Posted using GrabIt =----------------
------= Binary Usenet downloading made easy =---------
-= Get GrabIt for free from http://www.shemes.com/ =-
Click to expand...
 
"Marlowe" <MarlowedcNYET@earthlink.net> schrieb im Newsbeitrag
news:wFrse.5684$NX4.879@newsread1.news.pas.earthlink.net...
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.
Click to expand...
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.
 
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