Setting up a 12F683 to run at 20 Mhz

[johnnylynx]

I'm trying to get the 12F683 to run on an external crystal at 20 mhz...with no luck.

I've played with the OSCON and had it run at 1, 2, 4 and 8 Mhz. The Define command doesn't seem to do this though.

How do I setup the 12F683 for 20 mhz??????

Here is some code I'm playing with.

[HTML]'config_wdt_on
'config_fosc2_off
'config_fosc1_on
'config_fosc0_off
'config_ircf2_on
'config_ircf1_off
'config_ircf0_off
'define osc 20


'cfg %111111111111010
'osccon = %01001000 ' Osc set to 1 MHz
'osccon = %01100000 ' Osc set to 4 MHz
osccon = %01110000 ' Osc set to 8 MHz


trisio = %00011000 '
wpu = %00011000
CMCON0 = 7 ' Analog comparators off
ANSEL = 0 ' Analog select set to digital, pg 69 data
ADCON0 = 0 ' A/D turned OFF, pg 68 of data



pausetime var word
Out0 var gpio.0
Out1 var gpio.1
Out2 var gpio.2
B0 var byte

'input gpio.4

' SET VARIABLES
pausetime = 100
B0 = 0
low 0
low 1
low 2


start:

'button gpio.3,1,10,5,B0,1,notp
if gpio.3 = 1 then goto start

call blink0
call blink2
call blink1


goto start


blink0:
high out0
pause pausetime
low out0
'pause pausetime
return

blink1:
high out1
pause pausetime
low out1
'pause pausetime
return

blink2:
high out2
pause pausetime
low out2
'pause pausetime
return

notp:
goto start

end
[/HTML]

[mackrackit]

_HS_OSC
Needs to be used in the configs.
Then
DEFINE OSC 20
needs to be near the top of your code.

Have you read this thread?
http://www.picbasic.co.uk/forum/showthread.php?t=543

[johnnylynx]

_HS_OSC
Needs to be used in the configs.
Then
DEFINE OSC 20
needs to be near the top of your code.

Have you read this thread?
http://www.picbasic.co.uk/forum/showthread.php?t=543

I just looked at the link...Great information! Thanks for that.

I'll try your suggestions above today, really appreciate that too.

Do you know if the crystal and capacitor setup is 'touchy'? I'm trying to paste an image of the setup here...but not sure if you'll see it...

[johnnylynx]

_HS_OSC
Needs to be used in the configs.
Then
DEFINE OSC 20
needs to be near the top of your code.

Have you read this thread?
http://www.picbasic.co.uk/forum/showthread.php?t=543

OK, I tried the above but didn't work.

Trial 1:
- using the default setting of 4 mhz, the LED's flashed at rate 'X'

Trial 2:
- using the osccon = %01110000 (8 mhz)
- The LED's flashed at a rate of '2X'

Trial 3:
- Using the

_hs_osc
Define OSC 20

- the LED flashing rate went back to 'X'

It doesn't seem that the 20 Mhz is working??? Should it not flash at '5X' rate?

Here is what the top end of the code looks like now:

[HTML]

'*************************************
'Configuration Bits

_hs_osc

define osc 20

'osccon = %01001000 ' Osc set to 1 MHz
'osccon = %01100000 ' Osc set to 4 MHz
'osccon = %01110000 ' Osc set to 8 MHz


trisio = %00011000 '
' GPIO.5 output
' GPIO.4 input
' GPIO.3 input
' GPIO.2 output
' GPIO.1 output
' GPIO.0 output

wpu = %00010000
' GPIO.5 Weak pullup disabled
' GPIO.4 Weak pullup enabled
' GPIO.3 Weak pullup disabled
' GPIO.2 Weak pullup disabled
' GPIO.1 Weak pullup disabled
' GPIO.0 Weak pullup disabled

CMCON0 = 7 ' Analog comparators off
ANSEL = 0 ' Analog select set to digital, pg 69 data
ADCON0 = 0 ' A/D turned OFF, pg 68 of data


'***************************************
'Define Variables

pausetime var word
Out0 var gpio.0
Out1 var gpio.1
Out2 var gpio.2
B0 var byte

'***************************************
'Set Variables

pausetime = 100
B0 = 0
low 0
low 1
low 2
[/HTML]

[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 ).