16f88 internal oscillator

[merco]

hi,
i'm going to use 16F88 with internal oscillator.
I can't figure how can i select the 8 Mhz frequence with osctune
register...

Do you know it ?


thanks

 

[PeteS]

In the PIC16F87.88 datasheet on page 39, it states:

"The clock source frequency (INTOSC direct, INTRC
direct or INTOSC postscaler) is selected by configuring
the IRCF bits of the OSCCON register (page 40)."

It also states:
"The main output (INTOSC) is an 8 MHz clock source
which can be used to directly drive the system clock. It
also drives the INTOSC postscaler which can provide a
range of six clock frequencies from 125 kHz to 4 MHz."

So when we go to page 40....

we see:
000000 = Center frequency. Oscillator module is running at the
calibrated frequency.

Then when we move forward a little, to page 42 (clearly a typo in the
datasheet, but by reading everything we can find it)

We see:
REGISTER 4-2: OSCCON: OSCILLATOR CONTROL REGISTER (ADDRESS 8Fh)
Aha!! The register named above

So looking at the IRFC bits (as named above also) we see:
bit 7 Unimplemented: Read as '0'

bit 6-4 IRCF<2:0>: Internal RC Oscillator Frequency Select bits
000 = 31.25 kHz
001 = 125 kHz
010 = 250 kHz
011 = 500 kHz
100 = 1 MHz
101 = 2 MHz
110 = 4 MHz
111 = 8 MHz

bit 3 OSTS: Oscillator Start-up Time-out Status bit(1)
1 = Device is running from the primary system clock
0 = Device is running from T1OSC or INTRC as a secondary system clock
Note 1: Bit resets to '0' with Two-Speed Start-up mode and LP, XT
or HS selected as the
oscillator mode.

bit 2 IOFS: INTOSC Frequency Stable bit
1 = Frequency is stable
0 = Frequency is not stable

bit 1-0 SCS<1:0>: Oscillator Mode Select bits
00 = Oscillator mode defined by FOSC<2:0>
01 = T1OSC is used for system clock
10 = Internal RC is used for system clock
11 = Reserved

Datasheet at
http://ww1.microchip.com/downloads/en/DeviceDoc/30487c.pdf

Read the fascinating datasheet.

Cheers

PeteS

 

[Anthony Fremont]

hi,
i'm going to use 16F88 with internal oscillator.
I can't figure how can i select the 8 Mhz frequence with osctune
register...

Do you know it ?

I don't know of any way to do it with osctune, but you can load OSCCON
as documented in the datasheet. You may need to specify something like
_INTRC with your __CONFIG directive to make it work. I've had success
using the following code.

If you need ultra low power sleep current, then you should set the
oscillator to 32kHz. The datasheet doesn't say that, but I found it was
necessary to get the sleep current way down. The errata specifies other
problems with low sleep current, but didn't exactly seem to cover my
circumstances.

bsf STATUS, RP0 ; BANK 1

movlw b'01110000' ; Set internal osc to 8Mhz
movwf OSCCON & 0x7F

bcf STATUS, RP0 ; BANK 0

 

[merco]

thanks to all, ...i've lost my mind in the datasheet !