AT89LP428 datasheet(68/149 Pages) ATMEL

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3654A–MICRO–8/09

AT89LP428/828

Figure 13-5. CTC Mode Waveform Example

13.3.1.3

Dual-Slope Mode

The dual-slope mode occurs when CP/RL2 =0 and T2CM

1-0 = 1xB. In this mode the frequency

of the output is determined by the TOP value stored in RCAP2L and RCAP2H and output edges

occur at fractions of the timer period on both the up and down count. Figure 13-6 shows an

example of outputting two symmetrical waveforms using the toggle on match action. More com-

plex waveforms are achieved by changing the TOP value and the compare values more

frequently.

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

CP/RL2 = 1

CCA

{CCAH,CCAL}

{RCAP2H,RCA2L}

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

CCA

{CCAH,CCAL}

{CCBH,CCBL}

CCB

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