Setting up a 12F683 to run at 20 Mhz

[Charles Linquis]

When you set

'DEFINE OSC 20'

You are not "telling" the chip to run at 20MHz, you are telling PBP that
the chip is running at 20MHz (rather than 4MHz), and to adjust all pertinent
timing accordingly.

If the chip is actually running at 4MHz and you have DEFINE OSC 20, all the PBP PAUSES (and a lot of other timing, such as SERIN) will be off by a factor of 5. PBP uses a default define of 4MHz, so if you are actually running at 4MHz, you don't have to change this define. PAUSE 1000 will give a 1 second delay. If the PIC is actually running at 20MHz, then a PAUSE 1000 will give a 200 millisecond delay.
If you are running at any speed other than 4MHz, then you change the define accordingly.

[johnnylynx]

When you set

'DEFINE OSC 20'

You are not "telling" the chip to run at 20MHz, you are telling PBP that
the chip is running at 20MHz (rather than 4MHz), and to adjust all pertinent
timing accordingly.

If the chip is actually running at 4MHz and you have DEFINE OSC 20, all the PBP PAUSES (and a lot of other timing, such as SERIN) will be off by a factor of 5. PBP uses a default define of 4MHz, so if you are actually running at 4MHz, you don't have to change this define. PAUSE 1000 will give a 1 second delay. If the PIC is actually running at 20MHz, then a PAUSE 1000 will give a 200 millisecond delay.
If you are running at any speed other than 4MHz, then you change the define accordingly.

Ah, makes sense.

So in theory, if I use CFG_HS_OSC to get the 12F683 to use the external oscillator on pins 2&3 and use the DEFINE OSC 4 command...then the LED's should blink at the rate of 5X...right?

If so, I just tried that and the rate is still X???

What am I doing wrong?

Better yet...How do I confirm that the chip is running at 20Mhz??

John.

[Archangel]

Read this link: http://www.picbasic.co.uk/forum/showthread.php?t=543
Setting the config statement to HS controls the power supplied to the oscillator to "enable" it to run at high speed. The crystal determines that speed, The Define statement as Charles explained Syncs up the chips internal timing to the supplied crystal and Oscon allows you to alter the oscillator's prescaler in code (more or less ).

[johnnylynx]

Read this link: http://www.picbasic.co.uk/forum/showthread.php?t=543
Setting the config statement to HS controls the power supplied to the oscillator to "enable" it to run at high speed. The crystal determines that speed, The Define statement as Charles explained Syncs up the chips internal timing to the supplied crystal and Oscon allows you to alter the oscillator's prescaler in code (more or less ).

I'm not sure if you saw the photo I posted above...I'm using 2-27pF capacitors with the crystal. How can I confirm that the chip is running at 20Mhz?

John.

[Charles Linquis]

Run the program below -

Set the port to output

TOPP:
Toggle LED
PAUSE 1000
GOTO TOPP

If the LED stays on for one second and off for one second, then
you are running the frequency you have set in your DEFINE

For example:

IF have DEFINE OSC 4 -

and the above program turns the LED one second ON and one second OFF
Then you are running at 4MHz

If it is on for 200milliseconds at off for 200 milliseconds. Then you are running
at 20MHz.

[johnnylynx]

Run the program below -

Set the port to output

TOPP:
Toggle LED
PAUSE 1000
GOTO TOPP

If the LED stays on for one second and off for one second, then
you are running the frequency you have set in your DEFINE

For example:

IF have DEFINE OSC 4 -

and the above program turns the LED one second ON and one second OFF
Then you are running at 4MHz

If it is on for 200milliseconds at off for 200 milliseconds. Then you are running
at 20MHz.

I kinda thought that's what I had to do...just didn't believe it was that simple!

So I did that...even though I've 'told' the chip to run the external crystal and defined osc 4...I'm not blinking @ 200ms

Either the crystal isn't oscillating properly...or I should start flippin' burgers


BTW: The reason I'm trying to run this 12F683 at 20Mhz is to obtain readings from an accelerometer (aboard an RC aircraft) and control 3 servos all in a relatively smooth way.

In addition, I've bought XBEE 900 Mhz XSC transceivers and will be passing telemetry information from the aircraft to a ground station. I have more Q's about serial communications from the 12F683 to the XBEE...but that's for another thread. I first have to figure out what I don't know.

Cheers,

JOhn.

[mackrackit]

It does not look like you are setting the config correctly.
The thread that Joe and I pointed you to should have helped.

For now try going to the inc file for this chip in the PBP directory. Below is part of it.
If you are using PM for the assembler change
device pic12F683, intrc_osc_noclkout, wdt_on, mclr_on, protect_off
to
device pic12F683, hs_osc, wdt_on, mclr_on, protect_off

If you are using MPASM then change
__config _INTRC_OSC_NOCLKOUT & _WDT_ON & _MCLRE_ON & _CP_OFF
to
__config _HS_OSC & _WDT_ON & _MCLRE_ON & _CP_OFF

 device  pic12F683, intrc_osc_noclkout, wdt_on, mclr_on, protect_off

        XALL

        NOLIST

    else

        LIST

        LIST p = 12F683, r = dec, w = -302

        INCLUDE "P12F683.INC"	; MPASM  Header

        __config _INTRC_OSC_NOCLKOUT & _WDT_ON & _MCLRE_ON & _CP_OFF