PIC18LC658T-ESLASHCL datasheet(115/366 Pages) MICROCHIP

115 / 366 page

 2000 Microchip Technology Inc.

Advanced Information

DS30475A-page 115

PIC18CXX8

10.1

Timer0 Operation

Timer0 can operate as a timer or as a counter.

Timer mode is selected by clearing the T0CS bit. In

Timer mode, the Timer0 module will increment every

instruction cycle (without prescaler). If the TMR0L reg-

ister is written, the increment is inhibited for the follow-

ing two instruction cycles. The user can work around

this by writing an adjusted value to the TMR0L register.

Counter mode is selected by setting the T0CS bit. In

Counter mode, Timer0 will increment either on every

rising or falling edge of pin RA4/T0CKI. The increment-

ing edge is determined by the Timer0 Source Edge

Select bit (T0SE). Clearing the T0SE bit selects the ris-

ing edge. Restrictions on the external clock input are

discussed below.

When an external clock input is used for Timer0, it must

meet certain requirements. The requirements ensure

the external clock can be synchronized with the internal

phase clock (TOSC). Also, there is a delay in the actual

incrementing of Timer0 after synchronization.

10.2

Prescaler

An 8-bit counter is available as a prescaler for the

Timer0 module. The prescaler is not readable or

writable.

The PSA and T0PS2:T0PS0 bits determine the

prescaler assignment and prescale ratio.

Clearing bit PSA will assign the prescaler to the Timer0

module. When the prescaler is assigned to the Timer0

module, prescale values of 1:2, 1:4, ..., 1:256 are

selectable.

When assigned to the Timer0 module, all instructions

writing to the TMR0 register (e.g. CLRF

TMR0,

MOVWF TMR0, BSF TMR0, x

.... etc.) will clear the

prescaler count.

10.2.1

SWITCHING PRESCALER ASSIGNMENT

The prescaler assignment is fully under software con-

trol (i.e., it can be changed “on-the-fly” during program

execution).

Note:

Writing to TMR0 when the prescaler is

assigned to Timer0, will clear the prescaler

count but will not change the prescaler

assignment.

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