RFPIC12C509AF datasheet(48/104 Pages) MICROCHIP

48 / 104 page

rfPIC12C509AG/509AF

DS70031A-page 46

Preliminary

8.2.4

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 top of memory which contains the calibration value

for the internal RC oscillator. This location is never

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 cal-

ibration 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

OSCCAL, when written to with the calibration value, will

“trim” the internal oscillator to remove process variation

from the oscillator frequency.

For the rfPIC12C509AG/509AF bits <7:2>, CAL5-

CAL0 are used for calibration. Adjusting CAL5-0 from

000000 to 111111 yields a higher clock speed. Note that

bits 1 and 0 of OSCCAL are unimplemented and

should be written as 0 when modifying OSCCAL for

compatibility with future devices.

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; they are

unknown on 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 operation. 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 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.

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 read prior to

erasing the part. so it can be repro-

grammed correctly later.

RFPIC12C509AF Datasheet(PDF) 48 Page - Microchip Technology

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