64GA106 datasheet(122/330 Pages) MICROCHIP

122 / 330 page

PIC24FJ256GA110 FAMILY

DS39905E-page 122

 2010 Microchip Technology Inc.

8.5

Reference Clock Output

In addition to the CLKO output (FOSC/2) available in

certain oscillator modes, the device clock in the

PIC24FJ256GA110 family devices can also be config-

ured to provide a reference clock output signal to a port

pin. This feature is available in all oscillator configura-

tions and allows the user to select a greater range of

clock submultiples to drive external devices in the

application.

This reference clock output is controlled by the

REFOCON register (Register 8-4). Setting the ROEN

bit (REFOCON<15>) makes the clock signal available

on the REFO pin. The RODIV bits (REFOCON<11:8>)

enable the selection of 16 different clock divider

options.

The ROSSLP and ROSEL bits (REFOCON<13:12>)

control the availability of the reference output during

Sleep mode. The ROSEL bit determines if the oscillator

on OSC1 and OSC2, or the current system clock source,

is used for the reference clock output. The ROSSLP bit

determines if the reference source is available on REFO

when the device is in Sleep mode.

To use the reference clock output in Sleep mode, both

the ROSSLP and ROSEL bits must be set. The device

clock must also be configured for one of the Primary

Oscillator modes (EC, HS or XT); otherwise, if the

POSCEN bit is also not set, the oscillator on OSC1 and

OSC2 will be powered down when the device enters

Sleep mode. Clearing the ROSEL bit allows the refer-

ence output frequency to change as the system clock

changes during any clock switches.

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