DM163006 datasheet(23/320 Pages) MICROCHIP

23 / 320 page

 2001 Microchip Technology Inc.

Advance Information

DS39541A-page 23

PIC18C601/801

2.4

External Clock Input

The EC oscillator mode requires an external clock

source to be connected to the OSC1 pin. The feedback

device between OSC1 and OSC2 is turned off in these

modes to save current. There is no oscillator start-up

time required after a Power-on Reset or after a

recovery from SLEEP mode.

In the EC oscillator mode, the oscillator frequency

divided by 4 is available on the OSC2 pin. This signal

may be used for test purposes or to synchronize other

logic. Figure 2-3 shows the pin connections for the EC

oscillator mode.

FIGURE 2-3:

EXTERNAL CLOCK INPUT

OPERATION (EC OSC

CONFIGURATION)

2.5

HS4 (PLL)

A Phase Lock Loop (PLL) circuit is provided as a soft-

ware programmable option for users that want to multi-

ply the frequency of the incoming crystal oscillator

signal by 4. For an input clock frequency of 6 MHz, the

internal clock frequency will be multiplied to 24 MHz.

This is useful for customers who are concerned with

EMI due to high frequency crystals.

The PLL is enabled by configuring HS oscillator mode

and setting the PLLEN bit in the OSCON register. If HS

oscillator mode is not selected, or PLLEN bit in

OSCCON register is clear, the PLL is not enabled and

the system clock will come directly from OSC1. HS

oscillator mode is the default for PIC18C601/801. In all

other modes, the PLLEN bit and the SCS1 bit are

forced to ‘0’.

A PLL lock timer is used to ensure that the PLL has

locked before device execution starts. The PLL lock

timer has a time-out, referred to as TPLL.

FIGURE 2-4:

PLL BLOCK DIAGRAM

OSC1

OSC2

FOSC/4

Clock from

ext. system

PIC18C601/801

VCO

Loop

Filter

Feedback Divider

Crystal

Osc

OSCOUT

OSCIN

PLL Enable

FIN

FOUT

SYSCLK

Phase

Comparator

CVCO

HS Osc

DM163006 Datasheet(PDF) 23 Page - Microchip Technology

DM163006 Datasheet(HTML) 23 Page - Microchip Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

Datasheet Download

Link URL