PIC12C672 MICROCHIP [Microchip Technology], PIC12C672 Datasheet - Page 32

• Manufacturer Part Number: PIC12C672
• Description: 8-Pin, 8-Bit CMOS Microcontroller with EEPROM Data Memory
• Manufacturer: MICROCHIP [Microchip Technology]

PIC12CE5XX
8.2.5
The internal RC oscillator provides a fixed 4 MHz (nom-
inal) system clock at VDD = 5V and 25 C, see “Electri-
cal Specifications” section for information on variation
over voltage and temperature..
In addition, a calibration instruction is programmed into
the top of memory which contains the calibration value
for the internal RC oscillator. This value is programmed
as a MOVLW XX instruction where XX is the calibration
value, and is placed at the reset vector. This will load
the W register with the calibration value upon reset and
the PC will then roll over to the users program at
address 0x000. The user then has the option of writing
the value to the OSCCAL Register (05h) or ignoring it.
OSCCAL, when written to with the calibration value, will
“trim” the internal oscillator to remove process variation
from the oscillator frequency. .
For the PIC12CE518 and PIC12CE519, bits <7:4>,
CAL3-CAL0 are used for fine calibration while bit 3,
CALFST, and bit 2,CALSLW are used for more coarse
adjustment.
yields a higher clock speed. Set CALFST = 1 for
greater increase in frequency or set CALSLW = 1 for
greater decrease in frequency. Note that bits 1 and 0
of OSCCAL are unimplemented and should be written
as 0 when modifying OSCALL for compatibility with
future devices.
For the PIC12CE518 and PIC12CE519, the upper 4
bits of the register are used to allow for future, longer bit
length calibration schemes. Writing a larger value in
this location yields a higher clock speed.
8.3
The device differentiates between various kinds of
reset:
a) Power on reset (POR)
b) MCLR reset during normal operation
c) MCLR reset during SLEEP
d) WDT time-out reset during normal operation
e) WDT time-out reset during SLEEP
f) Wake-up from SLEEP on pin change
Some registers are not reset in any way; they are
unknown on POR and unchanged in any other reset.
Most other registers are reset to “reset state” on power-
on reset (POR), on MCLR, WDT or wake-up on pin
change reset during normal operation. They are not
affected by a WDT reset during SLEEP or MCLR reset
during SLEEP, since these resets are viewed as
DS40172A-page 32
Note:
INTERNAL 4 MHz RC OSCILLATOR
RESET
Please note that erasing the device will
also erase the pre-programmed internal
calibration value for the internal oscillator.
The calibration value must be saved prior
to erasing the part.
Adjusting CAL3-0 from 0000 to 1111
Preliminary
resumption of normal operation. The exceptions to this
are TO, PD, and GPWUF bits. They are set or cleared
differently in different reset situations. These bits are
used in software to determine the nature of reset. See
Table 8-3 for a full description of reset states of all
registers.
1997 Microchip Technology Inc.