Fosc PIC18F4620 Confused!

[Neyolight]

Hi

I have created another thread instead on the same topic as my question differs slightly. Im still confused on what frequency the PIC runs at with various modes.

Mode 1: External Oscillator connected to OSC1 and OSC2. A crystal of 16MHz is connected to OSC1 and OSC2 giving the frequency of oscillation (Fosc) of 16Mhz ( quite obviously). What confuses me is, in some diagrams ( PIC18F4620 Spec) you will see Fosc/4 coming out. Is Fosc/4 our frequency at which our code runs? I tried connected my PIC to 16Mhz crystal and see 16 Mhz at OSC1 and OSC2 ...Shouldnt OSC2 read Fosc/4 ( 4Mhz) ?

Mode 2: Selecting frequency via internal oscillator (OSC = INTIO67). Say I select 8Mhz....what is the frequency my code runs at? 8 or 8/4 Mhz?

Thanks

 

[keith1200rs]

See section 2.3 - the divide by 4 is only for EC mode, not crystal oscillator.

The clock is always divided by 4 to make the instruction cycle. So with and 8MHz clock the instructing cycle will be 500ns.

Keith

 

[Neyolight]

Using OSC= HS , One has to be in EC or ECIO mode...in both case Fosc is divided by 4? This means I should see Fosc/2 on OSC2 ?

Using an internal oscillator of 8Mhz...drops the frequency down to 2Mhz?

 

[keith1200rs]

HS uses an external crystal, EC uses an external clock. They are totally different modes. See section 2.1.

In every mode the raw clock is divided by 4 to get the instruction cycle.

Keith

 

[Neyolight]

Thanks Got it!

One last question --> INTIO67 ...Is that INTIO1 or INTIO2? My guess would be INTIO2 with I/O on A6 and A7

 

[keith1200rs]

There is no reference to INTIO67 in the datasheet so I assume you are talking about a function of the compiler you are using. It may vary from one make of compiler to the other, but the version I have has the following in the PIC18F4620.INC file:

;     OSC = RCIO6          External RC oscillator, port function on RA6
;     OSC = INTIO67        Internal oscillator block, port function on RA6 and RA7
;     OSC = INTIO7         Internal oscillator block, CLKOUT function on RA6, port function on RA7

Hopefully that answers the question.

Keith.

 

[Neyolight]

Yes, Thanks

 

[Neyolight]

There is no reference to INTIO67 in the datasheet so I assume you are talking about a function of the compiler you are using. It may vary from one make of compiler to the other, but the version I have has the following in the PIC18F4620.INC file:

;     OSC = RCIO6          External RC oscillator, port function on RA6
;     OSC = INTIO67        Internal oscillator block, port function on RA6 and RA7
;     OSC = INTIO7         Internal oscillator block, CLKOUT function on RA6, port function on RA7

Hopefully that answers the question.

Keith.

Where did you find this information about compiler from?

 

[keith1200rs]

By looking through the .INC file I referred to above. I don't know if it is just me, but I find compiler documentation is very poor and the only way to find things out is to rummage around the include files (and .H ones).

Keith