PIC12CE673-04SLASHP datasheet(48/116 Pages) MICROCHIP

48 / 116 page

PIC12CE67X

DS40181B-page 48

Preliminary

9.2.5

INTERNAL 4 MHz RC OSCILLATOR

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 last address of the program memory which contains

the calibration value for the internal RC oscillator. This

value is programmed as a RETLW XX instruction where

XX is the calibration value. In order to retrieve the cali-

bration value, issue a CALL YY instruction where YY is

the last location in program memory (03FFh for the

PIC12CE673, 07FFh for the PIC12CE674). Control will

be returned to the user’s program with the calibration

value loaded into the W register. The program should

then perform a MOVWF OSCCAL instruction to load

the value into the internal RC oscillator trim register.

OSCCAL, when written to with the calibration value, will

“trim” the internal oscillator to remove process variation

from the oscillator frequency. Only bits <7:2> of OSC-

CAL are implemented, and bits <1:0> should be written

as 0 for compatibility with future devices. The oscillator

calibration location is not code protected.

9.2.6

CLKOUT

The PIC12CE67X can be conﬁgured to provide a clock

out signal (CLKOUT) on pin 3 when the conﬁguration

word address (2007h) is programmed with FOSC2,

FOSC1, FOSC0 equal to 101 for INTRC or 111 for

EXTRC. The oscillator frequency, divided by 4 can be

used for test purposes or to synchronize other logic.

Note:

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.

9.3

Reset

The PIC12CE67X differentiates between various kinds

of reset:

• Power-on Reset (POR)

• MCLR reset during normal operation

• MCLR reset during SLEEP

• WDT Reset (normal operation)

Some registers are not affected in any reset condition;

their status is unknown on POR and unchanged in any

other reset. Most other registers are reset to a “reset

state” on Power-on Reset (POR), MCLR Reset, WDT

Reset, and MCLR Reset during SLEEP. They are not

affected by a WDT Wake-up, which is viewed as the

resumption of normal operation. The TO and PD bits

are set or cleared differently in different reset situations

as indicated in Table 9-4. These bits are used in

software to determine the nature of the reset. See

Table 9-5 for a full description of reset states of all

registers.

A simpliﬁed block diagram of the on-chip reset circuit is

shown in Figure 9-7.

The PIC12CE67X has a MCLR noise ﬁlter in the MCLR

reset path. The ﬁlter will detect and ignore small pulses.

It should be noted that a WDT Reset does not drive

MCLR pin low.

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