
2009 Microchip Technology Inc.
DS39636D-page 115
PIC18F2X1X/4X1X
10.0 TIMER0 MODULE
The Timer0 module incorporates the following features:
Software selectable operation as a timer or
counter in both 8-Bit or 16-Bit modes
Readable and writable registers
Dedicated 8-bit, software programmable
prescaler
Selectable clock source (internal or external)
Edge select for external clock
Interrupt-on-overflow
aspects of the module’s operation, including the
prescale selection. It is both readable and writable.
A simplified block diagram of the Timer0 module in 8-Bit
simplified block diagram of the Timer0 module in 16-Bit
mode.
REGISTER 10-1:
T0CON: TIMER0 CONTROL REGISTER
R/W-1
TMR0ON
T08BIT
T0CS
T0SE
PSA
T0PS2
T0PS1
T0PS0
bit 7
bit 0
bit 7
TMR0ON: Timer0 On/Off Control bit
1 = Enables Timer0
0 = Stops Timer0
bit 6
T08BIT: Timer0 8-bit/16-bit Control bit
1 = Timer0 is configured as an 8-bit timer/counter
0 = Timer0 is configured as a 16-bit timer/counter
bit 5
T0CS: Timer0 Clock Source Select bit
1 = Transition on T0CKI pin
0 = Internal instruction cycle clock (CLKO)
bit 4
T0SE: Timer0 Source Edge Select bit
1 = Increment on high-to-low transition on T0CKI pin
0 = Increment on low-to-high transition on T0CKI pin
bit 3
PSA: Timer0 Prescaler Assignment bit
1 = TImer0 prescaler is NOT assigned. Timer0 clock input bypasses prescaler.
0 = Timer0 prescaler is assigned. Timer0 clock input comes from prescaler output.
bit 2-0
T0PS2:T0PS0: Timer0 Prescaler Select bits
111 = 1:256 Prescale value
110 = 1:128 Prescale value
101 = 1:64 Prescale value
100 = 1:32 Prescale value
011 = 1:16 Prescale value
010 = 1:8
Prescale value
001 = 1:4
Prescale value
000 = 1:2
Prescale value
Legend:
R = Readable bit
W = Writable bit
U = Unimplemented bit, read as ‘0’
-n = Value at POR
‘1’ = Bit is set
‘0’ = Bit is cleared
x = Bit is unknown