PIC16LC73A-10/SO View Datasheet(PDF) - Microchip Technology

Part Name

Description

Manufacturer

PIC16LC73A-10/SO

8-Bit CMOS Microcontrollers with A/D Converter

Microchip Technology 

PIC16C7X

EXAMPLE 10-2: PWM PERIOD AND DUTY

CYCLE CALCULATION

Desired PWM frequency is 78.125 kHz,

Fosc = 20 MHz

TMR2 prescale = 1

1/78.125 kHz= [(PR2) + 1] • 4 • 1/20 MHz • 1

12.8 µs = [(PR2) + 1] • 4 • 50 ns • 1

In order to achieve higher resolution, the PWM fre-

quency must be decreased. In order to achieve higher

PWM frequency, the resolution must be decreased.

Table 10-3 lists example PWM frequencies and resolu-

tions for Fosc = 20 MHz. The TMR2 prescaler and PR2

values are also shown.

10.3.3 SET-UP FOR PWM OPERATION

PR2 = 63

Find the maximum resolution of the duty cycle that can

be used with a 78.125 kHz frequency and 20 MHz

oscillator:

1/78.125 kHz= 2PWM RESOLUTION • 1/20 MHz • 1

12.8 µs = 2PWM RESOLUTION • 50 ns • 1

256

= 2PWM RESOLUTION

log(256) = (PWM Resolution) • log(2)

8.0

= PWM Resolution

At most, an 8-bit resolution duty cycle can be obtained

from a 78.125 kHz frequency and a 20 MHz oscillator,

i.e., 0 ≤ CCPR1L:CCP1CON<5:4> ≤ 255. Any value

greater than 255 will result in a 100% duty cycle.

The following steps should be taken when configuring

the CCP module for PWM operation:

1. Set the PWM period by writing to the PR2 regis-

ter.

2. Set the PWM duty cycle by writing to the

CCPR1L register and CCP1CON<5:4> bits.

3. Make the CCP1 pin an output by clearing the

TRISC<2> bit.

4. Set the TMR2 prescale value and enable Timer2

by writing to T2CON.

5. Configure the CCP1 module for PWM operation.

TABLE 10-3: EXAMPLE PWM FREQUENCIES AND RESOLUTIONS AT 20 MHz

PWM Frequency

1.22 kHz 4.88 kHz 19.53 kHz 78.12 kHz 156.3 kHz 208.3 kHz

Timer Prescaler (1, 4, 16)

PR2 Value

Maximum Resolution (bits)

16

0xFF

10

4

0xFF

10

1

0xFF

10

1

0x3F

8

1

0x1F

7

1

0x17

5.5

TABLE 10-4: REGISTERS ASSOCIATED WITH CAPTURE, COMPARE, AND TIMER1

Address Name

Bit 7 Bit 6 Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

Value on:

POR,

BOR

Value on

all other

resets

0Bh,8Bh, INTCON

10Bh,18Bh

0Ch

0Dh(2)

PIR1

PIR2

8Ch

8Dh(2)

PIE1

PIE2

GIE PEIE T0IE

PSPIF(1,2) ADIF RCIF(2)

—

—

—

PSPIE(1,2) ADIE RCIE(2)

—

—

—

INTE

TXIF(2)

—

TXIE(2)

—

RBIE

T0IF INTF RBIF 0000 000x 0000 000u

SSPIF

—

SSPIE

—

CCP1IF TMR2IF TMR1IF 0000 0000 0000 0000

—

— CCP2IF ---- ---0 ---- ---0

CCP1IE TMR2IE TMR1IE 0000 0000 0000 0000

—

— CCP2IE ---- ---0 ---- ---0

87h

TRISC PORTC Data Direction Register

1111 1111 1111 1111

0Eh

TMR1L Holding register for the Least Significant Byte of the 16-bit TMR1 register

xxxx xxxx uuuu uuuu

0Fh

TMR1H Holding register for the Most Significant Byte of the 16-bit TMR1register

xxxx xxxx uuuu uuuu

10h

T1CON

—

— T1CKPS1 T1CKPS0 T1OSCEN T1SYNC TMR1CS TMR1ON --00 0000 --uu uuuu

15h

CCPR1L Capture/Compare/PWM register1 (LSB)

xxxx xxxx uuuu uuuu

16h

CCPR1H Capture/Compare/PWM register1 (MSB)

xxxx xxxx uuuu uuuu

17h

1Bh(2)

1Ch(2)

1Dh(2)

CCP1CON —

— CCP1X CCP1Y CCP1M3 CCP1M2 CCP1M1 CCP1M0 --00 0000 --00 0000

CCPR2L Capture/Compare/PWM register2 (LSB)

xxxx xxxx uuuu uuuu

CCPR2H Capture/Compare/PWM register2 (MSB)

xxxx xxxx uuuu uuuu

CCP2CON —

— CCP2X CCP2Y CCP2M3 CCP2M2 CCP2M1 CCP2M0 --00 0000 --00 0000

Legend: x = unknown, u = unchanged, - = unimplemented read as '0'. Shaded cells are not used by Capture and Timer1.

Note 1: Bits PSPIE and PSPIF are reserved on the PIC16C73/73A/76, always maintain these bits clear.

2: The PIC16C72 does not have a Parallel Slave Port, USART or CCP2 module, these bits are unimplemented, read as '0'.

© 1997 Microchip Technology Inc.

DS30390E-page 75

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