PIC18F44J10-ESLASHML datasheet(120/358 Pages) MICROCHIP

120 / 358 page

PIC18F45J10 FAMILY

DS39682C-page 118

Preliminary

11.3.2

TIMER1 OSCILLATOR LAYOUT

CONSIDERATIONS

The Timer1 oscillator circuit draws very little power

during operation. Due to the low-power nature of the

oscillator, it may also be sensitive to rapidly changing

signals in close proximity.

The oscillator circuit, shown in Figure 11-3, should be

located as close as possible to the microcontroller.

There should be no circuits passing within the oscillator

circuit boundaries other than VSS or VDD.

If a high-speed circuit must be located near the oscilla-

tor (such as the CCP1 pin in Output Compare or PWM

mode, or the primary oscillator using the OSC2 pin), a

grounded guard ring around the oscillator circuit, as

shown in Figure 11-4, may be helpful when used on a

single-sided PCB or in addition to a ground plane.

FIGURE 11-4:

OSCILLATOR CIRCUIT

WITH GROUNDED

GUARD RING

11.4

Timer1 Interrupt

The TMR1 register pair (TMR1H:TMR1L) increments

from 0000h to FFFFh and rolls over to 0000h. The

Timer1 interrupt, if enabled, is generated on overflow

which is

latched in interrupt

flag

bit, TMR1IF

(PIR1<0>). This interrupt can be enabled or disabled

by setting or clearing the Timer1 Interrupt Enable bit,

TMR1IE (PIE1<0>).

11.5

Resetting Timer1 Using the

ECCP/CCP Special Event Trigger

If ECCP1/CCP1 or CCP2 are configured to generate a

Special

Event

Trigger

in Compare

mode

(CCPxM3:CCPxM0 = 1011), this signal will reset

Timer1. The trigger from CCP2 will also start an A/D

conversion if the A/D module is enabled (see

Section 14.2.1 “Special Event Trigger” for more

information).

The module must be configured as either a timer or a

synchronous counter to take advantage of this feature.

When used this way, the CCPRH:CCPRL register pair

effectively becomes a period register for Timer1.

If Timer1 is running in Asynchronous Counter mode,

this Reset operation may not work.

In the event that a write to Timer1 coincides with a

Special Event Trigger, the write operation will take

precedence.

11.6

Using Timer1 as a Real-Time Clock

Adding an external LP oscillator to Timer1 (such as the

one described in Section 11.3 “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 supercapacitor 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 11-1, demonstrates a simple method to

increment a counter at one-second intervals using an

Interrupt Service Routine. Incrementing the TMR1

the routine which increments the seconds counter by

one. Additional counters for minutes and hours are

incremented as the previous counter overflows.

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

preload it. The simplest method is to set the MSb 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

routine, RTCinit. The Timer1 oscillator must also be

enabled and running at all times.

VDD

OSC1

VSS

OSC2

RC0

RC1

RC2

Note: Not drawn to scale.

Note:

The Special Event Triggers from the

ECCP1/CCPx module will not set the

TMR1IF interrupt flag bit (PIR1<0>).

PIC18F44J10-E/ML bảng dữ liệu(PDF) 120 Page - Microchip Technology

PIC18F44J10-E/ML bảng dữ liệu(HTML) 120 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

bảng dữ liệu tải về

Link URL