PIC18C658 MICROCHIP [Microchip Technology], PIC18C658 Datasheet - Page 115

• Manufacturer Part Number: PIC18C658
• Description: High-Performance Microcontrollers with CAN Module
• Manufacturer: MICROCHIP [Microchip Technology]

10.1
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 (T
incrementing of Timer0 after synchronization.
 2000 Microchip Technology Inc.
Timer0 Operation
OSC
). Also, there is a delay in the actual
Advanced Information
10.2
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
MOVWF TMR0, BSF TMR0, x.... etc.) will clear the
prescaler count.
10.2.1
The prescaler assignment is fully under software con-
trol (i.e., it can be changed “on-the-fly” during program
execution).
Note:
Prescaler
SWITCHING PRESCALER ASSIGNMENT
Writing to TMR0 when the prescaler is
assigned to Timer0, will clear the prescaler
count but will not change the prescaler
assignment.
PIC18CXX8
DS30475A-page 115
TMR0,