AT89LP428 datasheet(58/149 Pages) ATMEL

58 / 149 page

3654A–MICRO–8/09

AT89LP428/828

The timer overflow/underflow rate for up-down counting mode is the same as for up counting

mode, provided that the count direction does not change. Changes to the count direction may

result in longer or shorter periods between time-outs.

Figure 12-5. Timer 2 Waveform: Auto-reload Mode (DCEN = 1)

12.3.3

Dual Slope Counter

When Timer 2 Auto-reload mode uses Count Mode 2 (T2CM

1-0 = 10B) or Count Mode 3

(T2CM

1-0 = 11B), the timer operates in a dual slope fashion. The timer counts up from

MIN to TOP and then counts down from TOP to MIN, following a sawtooth waveform as shown

in Figure 12-6. The EXF2 bit is set/cleared by hardware to reflect the current count direction

(Up = 0 and Down = 1). The value of TOP stored in RCAP2H and RCAP2L is double-buffered

such that a new TOP value takes affect only after an underflow. The only difference between

Mode 2 and Mode 3 is when the interrupt flag is set. In Mode 2, TF2 is set once per count period

when the timer underflows at MIN. In Mode 3, TF2 is set twice per count period, once when the

timer overflows at TOP and once when the timer underflows at MIN. The interrupt service routine

can check the EXF2 bit to determine if TF2 was set at TOP or MIN. These count modes are pro-

vided to support variable precision symmetrical PWM in the CCA. DCEN has no effect when

using dual slope operation. The Timer 2 overflow rate for this mode is given in the following

equation:

Max

Min

Bottom

T2CM1-0 = 00B, DCEN = 1

Max

Min

Top

T2CM1-0 = 01B, DCEN = 1

T2EX

TF2 Set

EXF2

Auto-Reload Mode:

DCEN = 0, T2CM = 10B

Time-out Period

RCAP2H RCAP2L

}

Oscillator Frequency

-------------------------------------------------------------------

TPS

()

AT89LP428 датащи(PDF) 58 Page - ATMEL Corporation

AT89LP428 датащи(HTML) 58 Page - ATMEL Corporation

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

датащи скачать

ссылки URL