Setting 8Mhz clock speed on PIC16F684

Can someone kindly help me please?

I am trying to make a PIC16F684 run at 8Mhz instead of the default 4Mhz.

Problem is, test led's just keeping flashing at 10 secs...

I have MPASM ticked as the Compiler/Assembler and using PBP 2.60

Simple code below:

@ __config _INTOSCIO & _WDT_OFF

DEFINE OSC 8

OSCCON = %01110000 ' Internal 8MHz osc
'OSCTUNE = %00000000 ' not in use
ANSEL = %00000000 'Disable analog select so ports work as digital i/o.
CMCON0 = %00000111 'Disable analog comparators.
TRISA = %00000000 'Set PORTA as OUTPUT.
PORTA = %00000000 'Set PORTA pins all low.


Start

main:

HIGH PORTA.2
PAUSE 10000
LOW PORTA.2
PAUSE 2000
HIGH PORTA.2
PAUSE 10000
LOW PORTA.2
PAUSE 2000

goto main

Quote:

---

Problem is, test led's just keeping flashing at 10 secs...

---

PAUSE 10000 is 10 seconds

if the osc is 8 mhz and you tell the compiler the osc is 8 mhz with DEFINE OSC 8
then the pause is 10 seconds as requested

what do you expect the result to be ?

Hi Richard, thanks for the reply.

"what do you expect the result to be ?"

I thought (and was hoping) that double the OSC speed from 4 to 8Mhz would drive the led's twice as fast, 10secs would become five at 8Mhz if you see what I mean.

Dave

Just to add, I based my last post on this article: http:// melabs.com/resources/pbpmanual/7_0.htm

But I may have misinterpreted it, in that I thought PAUSE 1000 with DEFINE OSC 4 internal OSC would give one second delay and pause 1000 with DEFINE OSC 8 internal OSC would give 0.5 second delay.....

So are we saying that the above PAUSE 1000 would both cause a one second delay?

Is it only external Xtals/resonators that throw the internal timing off?

Dave

Quote:

---

Is it only external Xtals/resonators that throw the internal timing off?

---

no not at all.

the only time it fails is when DEFINE OSC does not match the real osc frequency.

Thanks again Richard.

So as long as I use DEFINE OSC X, PB knows and compensates for the change still giving the correct timings PAUSE etc?

David

Yes, That is correct. The PAUSE command is based on the OSC frequency. If you had an 4 Mhz. crystal connected and told PBP that the OSC was 8Mhz. the PAUSE command would give you 2 times the value entered into the PAUSE command.

Dave & Richard, thank you both for taking the time to reply, much appreciated.

Dave