AT89LP6440 datasheet(76/194 Pages) ATMEL

76 / 194 page

3706A–MICRO–9/09

AT89LP6440 - Preliminary

Figure 13-6. Dual-Slope Waveform Example

13.3.2

Timer 2 Operation for Compare Mode

Compare channels will work with any Timer 2 operating mode. The full 16-bit compare range

may not be available in all modes. In order for a compare output action to take place, the com-

pare values must be within the counting range of Timer 2. CTCx must be cleared to 0 for all

channels if Timer 2 is operating in Baud Rate mode or errors may occur in the serial

communication.

13.4

Pulse Width Modulation Mode

In Pulse Width Modulation (PWM) Mode, a compare channel can output a square wave with pro-

grammable frequency and duty cycle. Setting CCMx = 1 and CxM

2-0 = 10xB enables PWM

Mode. PWM Mode is similar to Output Compare Mode except that the compare value is double-

buffered. A diagram of a CCA channel in PWM Mode is shown in Figure 13-7. The PWM polarity

is selectable between inverting and non-inverting modes. PWM is intended for use with Timer 2

in Auto-Reload Mode (CP/RL2 =0, DCEN = 0) using count modes 1, 2 or 3. The PWM can oper-

ate in asymmetric (edge-aligned) or symmetric (center-aligned) mode depending on the T2CM

selection. The CCA PWM has variable precision from 2 to 16 bits. A trade-off between frequency

and precision is made by changing the TOP value of the timer. The CCA PWM always uses the

greatest precision allowable for the selected output frequency, as compared to Timer 0 and 1

whose PWMs are fixed at 8-bit precision regardless of frequency.

Figure 13-7. CCA PWM Mode Diagram

{RCAP2H,RCA2L}

CP/RL2 = 0, T2CM1-0 = 10B, DCEN = 0

CCA

{CCAH,CCAL}

{CCBH,CCBL}

CCB

TL2

TH2

CCxL

CCxH

CCCx

Interrupt

CCx (P2.x)

T2CCC

T2CCL

shadow

CCFx

CIENx

CxM2-0

T2CCH

shadow

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