Sergei Shirokov wrote:
>
> Hello all
> Can anyone explain me how works the OSCCAL reg. when internal 4Mhz
> oscilator mode of pic12c508 activated?


Sergei:

The data sheet (DS40139A-page 28) says that the first instruction
to be executed at reset is MOVLW XX where XX is the cal value.  The
PC then rolls over to 00 which is the normal reset start address. At
this time the W register will contain the XX osc cal value.  Before
the W register is changed it should be writtin to the OSCCAL register
(05h).  The value in OSCCAL then adjusts the frequency.  Pages 61-63
have graphs showing that the oscillator Freq-vs-temp and Vdd.
An OSCCAL change of one bit causes about 4nS change.

Have Fun,
Brooke