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PIC2620/4620 and 2520 datasheets wrong?

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Boomslang

Member
Hi All

In OCSTUNE TUN4:TUN0. That is 5 bits, but in the datasheet it shows 6 bits??? It also shows the 6th bit as unimplemented? I dont have a scope to test if it does in fact use 6 bits to change the OSC speed.

Can anyone of you shed some light on it please?
 

Pommie

Well-Known Member
Most Helpful Member
When in doubt check the device file,

sfr (key=OSCTUNE addr=0xf9b size=1 access='rw rw u rw rw rw rw rw')
reset (por='00-00000' mclr='0--00000')
bit (names='HF256DIV PLLEN - TUN' width='1 1 1 5')
stimulus (scl=rwb pcfiles=rw regfiles=w)

So, it's 5 bits in total.

You'll find the dev file in C:\Program Files\Microchip\MPLAB IDE\Device

Mike.
 

Pommie

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Most Helpful Member
BTW, if you're trying to use the PLL with the internal oscillator you must set OSCCON to 0x60 or 0x70. Setting it to 0x62 or 0x72 stops the PLL from functioning. This is not mentioned in the DS anywhere and had me pulling my hair out.

Mike.
 

Pommie

Well-Known Member
Most Helpful Member
How are you going to adjust your clock? How will you know if it's running slow or fast? Most applications are happy with the 1% accuracy or use a crystal.

Mike.
 

Pommie

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Most Helpful Member
You can tune the clock, you just can't select the internal oscillator in OSCCON (not OSCTUN). You have to select primary oscillator and select internal in the config.

Mike.
 

Boomslang

Member
I am building a chronograph, so the adjustment will be once off when calibrating it. I need around +-5% adjustment.

BTW I have it running at 8MHz X 4xPPL = 32MHz. I know that part is working as I used some code from one of my old projects.
 
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Pommie

Well-Known Member
Most Helpful Member
The internal oscillator will vary with temperature, Vdd and the colour of the sky. If you're making a chronograph I would add a 32kHz crystal as the timer 1 oscillator. You then have a very accurate timer 1 and up to 32MHz internal frequency.

Edit, change that to a 38k crystal if you want a 100Hz or 1kHz interrupt.

Mike.
 
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