How to verify HS_PLL clock speed

[Bruce]

The easiest way I know to check would be with an LED & a few pause statements. If HSPLL isn't running it will be obvious on the LED.

Main:
HIGH LED
PAUSE 500
LOW LED
PASE 500
GOTO Main

OSC2 can output the clock/4, but only in EC mode. In other modes, the signal from OSC2 output is so weak you'll load it with a scope probe.

[CocaColaKid]

Would this not enable the x4 PLL?

@ __CONFIG _CONFIG1H, _OSCS_OFF_1H & _HSPLL_OSC_1H
@ __CONFIG _CONFIG2L, _BOR_ON_2L & _PWRT_ON_2L & _BORV_45_2L
@ __CONFIG _CONFIG2H, _WDT_ON_2H 
@ __CONFIG _CONFIG4L, _STVR_ON_4L & _LVP_OFF_4L & _DEBUG_OFF_4L

[Bruce]

It should, but check this with your programmer before programing that part.

Also, you might want to use the osc resistor shown in the datasheet since this may be over driving your crystal. HS uses a higher drive output on OSC2.

[CocaColaKid]

I'm actually using a TTL oscillator so this shouldn't be an issues should it?

[Bruce]

"EDIT"

For OSC2 to output clock/4 with a TTL clock oscillator, you'll need to use EC or ECIO mode.

HSPLL isn't available for EC or ECIO mode. With a 4MHz TTL clock oscillator, you'll have only 4MHz. HSPLL mode works with the TTL clock if you set config fuses for HSPLL, but you can't use the OSC2 pin in HS mode. Only EC or ECIO modes.

[CocaColaKid]

ah, I'll drop in a crystal then, I have both at my disposable.

[Bruce]

You know, it's not really 100% clear from the datasheet, but looking at Figure 2-2, it does appear an external clock, I.E. a TTL osc can be input to OSC1, and you can select HS, XT or LP modes, so it "appears" you can use a TTL clock in on OSC1, and still make use of the HSPLL as long as you have HS set in config.

I'll have to experiment with that one.