PIC17C752-08SLASHP datasheet(94/320 Pages) MICROCHIP

94 / 320 page

PIC17C75X

DS30264A-page 94

Preliminary

13.1 Timer1 and Timer2

13.1.1

TIMER1, TIMER2 IN 8-BIT MODE

Both Timer1 and Timer2 will operate in 8-bit mode

when the T16 bit is clear. These two timers can be inde-

pendently conﬁgured to increment from the internal

instruction cycle clock (TCY) or from an external clock

source on the RB4/TCLK12 pin. The timer clock source

is conﬁgured by the TMRxCS bit (x = 1 for Timer1 or =

2 for Timer2). When TMRxCS is clear, the clock source

is internal and increments once every instruction cycle

(Fosc/4). When TMRxCS is set, the clock source is the

RB4/TCLK12 pin, and the counters will increment on

every falling edge of the RB4/TCLK12 pin.

The timer increments from 00h until it equals the Period

ment cycle. The timer interrupt ﬂag is set when the

timer is reset. TMR1 and TMR2 have individual inter-

rupt ﬂag bits. The TMR1 interrupt ﬂag bit is latched into

TMR1IF, and the TMR2 interrupt ﬂag bit is latched into

TMR2IF.

Each timer also has a corresponding interrupt enable

bit (TMRxIE). The timer interrupt can be enabled/dis-

abled by setting/clearing this bit. For peripheral inter-

rupts to be enabled, the Peripheral Interrupt Enable bit

must be set (PEIE = '1') and global interrupt must be

enabled (GLINTD = '0').

The timers can be turned on and off under software

control. When the timer on control bit (TMRxON) is set,

the timer increments from the clock source. When

TMRxON is cleared, the timer is turned off and cannot

cause the timer interrupt ﬂag to be set.

13.1.1.1

EXTERNAL CLOCK INPUT FOR TIMER1

AND TIMER2

When TMRxCS is set, the clock source is the

RB4/TCLK12 pin, and the counter will increment on

every falling edge on the RB4/TCLK12 pin. The

TCLK12 input is synchronized with internal phase

clocks. This causes a delay from the time a falling edge

appears on TCLK12 to the time TMR1 or TMR2 is actu-

ally incremented. For the external clock input timing

requirements, see the Electrical Speciﬁcation section.

FIGURE 13-4: TIMER1 AND TIMER2 IN TWO 8-BIT TIMER/COUNTER MODE

Fosc/4

RB4/TCLK12

TMR1ON

(TCON2<0>)

TMR1CS

(TCON1<0>)

TMR1

PR1

Reset

Equal

Set TMR1IF

(PIR1<4>)

Comparator<8>

Comparator x8

Fosc/4

TMR2ON

(TCON2<1>)

TMR2CS

(TCON1<1>)

TMR2

PR2

Reset

Equal

Set TMR2IF

(PIR1<5>)

Comparator<8>

Comparator x8

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