PIC18F010T-I/SN 查看數據表（PDF） - Microchip Technology

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PIC18F010T-I/SN

High Performance Microcontrollers

Microchip Technology 

PIC18F010/020

2.6 Two-Speed Clock Start-up Mode

In order to minimize the latency between oscillator

start-up and code execution, a mode which allows the

system clock to initially use the internal clock, may be

selected with IESO (Internal-External Switchover) bit.

In this mode and upon RESET, the system will begin

execution with the internal oscillator at the frequency

selected by the IRCFx bits of the OSCCON register.

Note:

Only on Power-on Reset, the register con-

tents are zeroed by the POR circuitry and

the frequency selection is forced to 32 kHz.

The register is not effected by any other

forms of RESET.

After the OST has timed out, a glitchless switchover will

be made to the oscillator mode selected by FOSCx in

the CONFIG1H register. The software may read the

OSTO bit to determine when the switchover takes

place, so that any software timing delays may be

adjusted.

Wake-up from SLEEP causes a unique start-up proce-

dure. The power supply is assumed to be stable, since

neither the POR nor the BOR Resets have been

invoked. This assumption allows the Power-on Timer

(PWRT) time-out to be bypassed, and only the OST

time-out to be used. This results in almost immediate

code execution with the minimum of delay. The internal

oscillator frequency can be selected to be close to final

crystal frequency to reduce timing differences, or a lower

frequency can be chosen to reduce power consumption.

REGISTER 2-1: OSCCON REGISTER (ADDRESS FD3h)

U-0

R/W-0 R/W-0 R/W-0

R-0

R/W-0

U-0

R/W-0

—

IRCF2 IRCF1 IRCF0

OSTO

IESO

—

SCS

bit 7

bit 0

bit 7

bit 6-4

bit 3

bit 2

bit 1

bit 0

Unimplemented: Read as ‘0’

IRCF<2:0>: Internal Oscillator Frequency Select bits

000 = 32 kHz

001 = Reserved

010 = Reserved

011 = 500 kHz

100 = 1 MHz

101 = Reserved

110 = 4 MHz

111 = 8 MHz

OSTO: Oscillator Start-up Time-out Status bit

1 = Oscillator Start-up Timer has timed out

0 = Oscillator Start-up Timer running

IESO: Internal-External Switchover bit

1 = Start with internal oscillator, then switch over to selected oscillator mode after OST

0 = No switch from internal oscillator from RESET

Unimplemented: Read as ‘0’

SCS: System Clock Switch bit

1 = Clock source comes from internal oscillator input

0 = Clock source comes from external clock source on OSC1

Legend:

R = Readable bit

- n = Value at POR

W = Writable bit

’1’ = Bit is set

U = Unimplemented bit, read as ‘0’

’0’ = Bit is cleared x = Bit is unknown

Note: This register must be unlocked to modify, see Section 12.4.

DS41142A-page 10

Preliminary

 2001 Microchip Technology Inc.

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