PIC12F519 Datasheet, PDF (41/88 Pages) Microchip Technology – 8-Pin, 8-Bit Flash Microcontroller

8.2.5
INTERNAL 4/8 MHz RC
OSCILLATOR
The internal RC oscillator provides a fixed 4/8 MHz
(nominal) system clock at VDD = 5V and 25°C, (see
Section 11.0 “Electrical Characteristics” for
information on variation over voltage and temperature).
In addition, a calibration instruction is programmed into
the last address of memory, which contains the calibra-
tion value for the internal RC oscillator. This location is
always non-code protected, regardless of the
code-protect settings. 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.
Note:
Erasing the device will also erase the
pre-programmed internal calibration value
for the internal oscillator. The calibration
value must be read prior to erasing the
part so it can be reprogrammed correctly
later.
For the PIC12F519 device, only bits <7:1> of OSCCAL
are used for calibration. See Register 4-3 for more
information.
Note:
The bit 0 of the OSCCAL register is
unimplemented and should be written as
‘0’ when modifying OSCCAL for
compatibility with future devices.
PIC12F519
8.3 Reset
The device differentiates between various kinds of
Reset:
• Power-on Reset (POR)
• MCLR Reset during normal operation
• MCLR Reset during Sleep
• WDT Time-out Reset during normal operation
• WDT Time-out Reset during Sleep
• Wake-up from Sleep on pin change
Some registers are not reset in any way, and they are
unknown on Power-on Reset (POR) and unchanged in
any other Reset. Most other registers are reset to
“Reset state” on Power-on Reset (POR), MCLR, WDT
or Wake-up on pin change Reset during normal opera-
tion. They are not affected by a WDT Reset during
Sleep or MCLR Reset during Sleep, since these
Resets are viewed as resumption of normal operation.
The exceptions to this are TO, PD and RBWUF bits.
They are set or cleared differently in different Reset sit-
uations. 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.
© 2007 Microchip Technology Inc.
Preliminary
DS41319A-page 39