PIC18F6X2X datasheet(164/386 Pages) MICROCHIP

164 / 386 page

PIC18F6X2X/8X2X

DS39612A-page 162

Advance Information

 2003 Microchip Technology Inc.

17.1.3

ECCP MODULES AND TIMER

RESOURCES

Like the standard CCP modules, the ECCP modules

can utilize Timers 1, 2, 3 or 4, depending on the mode

selected. Timer1 and Timer3 are available for modules

in Capture or Compare modes, while Timer2 and

Timer4 are available for modules in PWM mode. Addi-

tional details on timer resources are provided in

Section 16.1.1.

17.2

Capture and Compare Modes

Except for the operation of the special event trigger dis-

cussed below, the Capture and Compare modes of the

ECCP module are identical in operation to that of

CCP4. These are discussed in detail in Section 16.2

and Section 16.3.

17.2.1

SPECIAL EVENT TRIGGER

In this mode, an internal hardware trigger is generated

in Compare mode, on a match between the CCPR reg-

ister pair and the selected timer. This can be used in

turn to initiate an action.

The special event trigger output of either ECCP1 or

ECCP2 resets the TMR1 or TMR3 register pair,

depending on which timer resource is currently

selected. This allows the CCPRx register to effectively

be a 16-bit programmable period register for Timer1 or

Timer3. In addition, the ECCP2 special event trigger

will also start an A/D conversion if the A/D module is

enabled.

The triggers are not implemented for ECCP3, CCP4 or

CCP5.

Selecting

the

Special

Event

mode

(CCPxM3:CCPxM0 = 1011) for these modules has the

same effect as selecting the Compare with Software

Interrupt mode (CCPxM3:CCPxM0 = 1010).

17.3

Standard PWM Mode

When configured in Single Output mode, the ECCP

module functions identically to the standard CCP

module in PWM mode as described in Section 16.4.

This is also sometimes referred to as “Compatible

CCP” mode as in Tables 17-1 through 17-3.

17.4

Enhanced PWM Mode

The Enhanced PWM mode provides additional PWM

output options for a broader range of control applica-

tions. The module is a backward compatible version of

the standard CCP module and offers up to four outputs,

designated PxA through PxD. Users are also able to

select the polarity of the signal (either active high or

active low). The module’s output mode and polarity

are configured

setting

the

PxM1:PxM0

and

CCPxM3CCPxM0 bits of the CCPxCON register

(CCPxCON<7:6> and CCPxCON<3:0>, respectively).

For the sake of clarity, Enhanced PWM mode operation

is described generically throughout this section with

respect to ECCP1 and TMR2 modules. Control register

names are presented in terms of ECCP1. All three

enhanced modules, as well as the two timer resources,

can be used interchangeably and function identically.

TMR2 or TMR4 can be selected for PWM operation by

selecting the proper bits in T3CON.

Figure 17-1 shows a simplified block diagram of PWM

operation. All control registers are double-buffered and

are loaded at the beginning of a new PWM cycle (the

period boundary when Timer2 resets) in order to pre-

vent glitches on any of the outputs. The exception is the

PWM delay register, ECCP1DEL, which is loaded at

either the duty cycle boundary or the boundary period

(whichever comes first). Because of the buffering, the

module waits until the assigned timer resets instead of

starting immediately. This means that enhanced PWM

waveforms do not exactly match the standard PWM

waveforms but are instead offset by one full instruction

cycle (4 TOSC).

As before, the user must manually configure the

appropriate TRIS bits for output.

17.4.1

PWM PERIOD

The PWM period is specified by writing to the PR2

equation:

PWM frequency is defined as 1 / [PWM period]. When

TMR2 is equal to PR2, the following three events occur

on the next increment cycle:

•TMR2 is cleared

• The CCP1 pin is set (if PWM duty cycle = 0%, the

CCP1 pin will not be set)

• The PWM duty cycle is copied from CCPR1L into

CCPR1H

Note:

The special event trigger from ECCP2 will

not set the Timer1 or Timer3 interrupt flag

bits.

Note:

When setting up single output PWM opera-

tions, users are free to use either of the

processes described in Section 16.4.3 or

Section 17.4.9. The latter is more generic

but will work for either single or multi-output

PWM.

Note:

The Timer2 postscaler (see Section 13.0)

is not used in the determination of the

PWM frequency. The postscaler could be

used to have a servo update rate at a

different frequency than the PWM output.

PWM Period = [(PR2) + 1] • 4 • TOSC •

(TMR2 Prescale Value)

PIC18F6X2X Datasheet(PDF) 164 Page - Microchip Technology

PIC18F6X2X Datasheet(HTML) 164 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

Datasheet Download

Link URL