PIC16F88-ISLASHSS datasheet(78/214 Pages) MICROCHIP

78 / 214 page

PIC16F87/88

DS30487B-page 76

Preliminary

 2003 Microchip Technology Inc.

7.9

Resetting Timer1 Register Pair

(TMR1H, TMR1L)

TMR1H and TMR1L registers are not reset to 00h on a

POR, or any other RESET, except by the CCP1 special

event triggers.

T1CON register is reset to 00h on a Power-on Reset or

a Brown-out Reset, which shuts off the timer and

leaves a 1:1 prescale. In all other RESETS, the register

is unaffected.

7.10

Timer1 Prescaler

The prescaler counter is cleared on writes to the

TMR1H or TMR1L registers.

7.11

Using Timer1 as a Real-Time

Clock

Adding an external LP oscillator to Timer1 (such as the

one described in Section 7.6 “Timer1 Oscillator”,

above), gives users the option to include RTC function-

ality to their applications. This is accomplished with an

inexpensive watch crystal to provide an accurate time

base, and several lines of application code to calculate

the time. When operating in SLEEP mode and using a

battery or super capacitor as a power source, it can

completely eliminate the need for a separate RTC

device and battery backup.

The application code routine, RTCisr, shown in

Example 7-3, demonstrates a simple method to incre-

ment a counter at one-second intervals using an Inter-

rupt Service Routine. Incrementing the TMR1 register

pair to overflow triggers the interrupt and calls the rou-

tine, which increments the seconds counter by one;

additional

counters

for

minutes

and

hours

are

incremented as the previous counter overflow.

Since the register pair is 16-bits wide, counting up to

overflow the register directly from a 32.768 kHz clock

would take 2 seconds. To force the overflow at the

required one-second intervals, it is necessary to pre-

load it; the simplest method is to set the MSbit of

TMR1H with a BSF instruction. Note that the TMR1L

introduce cumulative error over many cycles.

For this method to be accurate, Timer1 must operate in

Asynchronous mode, and the Timer1 overflow interrupt

must be enabled (PIE1<0> = 1), as shown in the rou-

tine, RTCinit. The Timer1 oscillator must also be

enabled and running at all times.

PIC16F88-I/SS 데이터시트(PDF) 78 Page - Microchip Technology

PIC16F88-I/SS 데이터시트(HTML) 78 Page - Microchip Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

데이터시트 다운로드

링크 URL