PIC18F258-ESLASHLSQTP datasheet(136/402 Pages) MICROCHIP

136 / 402 page

PIC18FXX8

DS41159E-page 134

16.4

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 15.4

“PWM Mode”. The differences in registers and ports

are as described in Section 16.2 “Capture Mode”. In

addition, the two Least Significant bits of the 10-bit

PWM

duty

cycle

value

are

represented

ECCP1CON<5:4>.

16.5

Enhanced PWM Mode

The Enhanced PWM mode provides additional PWM

output options for a broader range of control applica-

tions. The module is an upwardly compatible version of

the standard CCP module and is modified to provide up

to four outputs, designated P1A through P1D. 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

EPWM1M1:EPWM1M0 and ECCP1M3:ECCP1M0 bits

of the ECCP1CON register (ECCP1CON<7:6> and

ECCP1CON<3:0>, respectively).

Figure 16-1 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 the assigned timer resets) in

order to prevent 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 TRISD bits for output.

16.5.1

PWM OUTPUT CONFIGURATIONS

The EPWM1M<1:0> bits in the ECCP1CON register

allow one of four configurations:

• Single Output

• Half-Bridge Output

• Full-Bridge Output, Forward mode

• Full-Bridge Output, Reverse mode

The Single Output mode is the standard PWM mode

discussed in Section 15.4 “PWM Mode”. The Half-

Bridge and Full-Bridge Output modes are covered in

detail in the sections that follow.

The

general

relationship

the

outputs

all

configurations is summarized in Figure 16-2.

FIGURE 16-1:

SIMPLIFIED BLOCK DIAGRAM OF THE ENHANCED PWM MODULE

Note:

When setting up single output PWM

operations, users are free to use either of

the processes described in Section 15.4.3

“Setup

for

PWM

Operation”

Section 16.5.8 “Setup for PWM Opera-

tion”. The latter is more generic, but will

work for either single or multi-output PWM.

ECCPR1L

ECCPR1H (Slave)

Comparator

TMR2

Comparator

PR2

(Note 1)

Duty Cycle Registers

ECCP1CON<5:4>

Clear Timer,

set ECCP1 pin and

latch D.C.

Note:

The 8-bit TMR2 register is concatenated with the 2-bit internal Q clock, or 2 bits of the prescaler, to create the 10-bit time base.

TRISD<4>

RD4/PSP4/ECCP1/P1A

TRISD<5>

RD5/PSP5/P1B

TRISD<6>

RD6/PSP6/P1C

TRISD<7>

RD7/PSP7/P1D

Output

Controller

EPWM1M1<1:0>

ECCP1M<3:0>

ECCP1DEL

ECCP1/P1A

P1B

P1C

P1D

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