AT89LP428 datasheet(56/149 Pages) ATMEL

56 / 149 page

3654A–MICRO–8/09

AT89LP428/828

12.3.1

Up Counter

Figure 12-2 shows Timer 2 automatically counting up when DCEN = 0 and T2CM

1-0 = 00B. In

this mode Timer 2 counts up to MAX and then sets the TF2 bit upon overflow. The overflow also

causes the timer registers to be reloaded with BOTTOM, the 16-bit value in RCAP2H and

RCAP2L. If EXEN2 = 1, a 16-bit reload can be triggered either by an overflow or by a 1-to-0 tran-

sition at external input T2EX. This transition also sets the EXF2 bit. Both the TF2 and EXF2 bits

can generate an interrupt. The Timer 2 overflow rate for this mode is given in the following

equation:

Timer 2 may also be configured to count from MIN to TOP instead of BOTTOM to MAX by set-

ting T2CM

1-0 = 01B. In this mode Timer 2 counts up to TOP, the 16-bit value in RCAP2H and

RCAP2L and then overflows. The overflow sets TF2 and causes the timer registers to be

reloaded with MIN. If EXEN2 = 1, a 1-to-0 transition on T2EX will clear the timer and set EXF2.

The Timer 2 overflow rate for this mode is given in the following equation:

Timer 2 Count Mode 1 is provided to support variable precision asymmetrical PWM in the CCA.

The value of TOP stored in RCAP2H and RCAP2L is double-buffered such that a new TOP

value takes affect only after an overflow. The behavior of Count Mode 0 versus Count Mode 1 is

shown in Figure 12-3.

Figure 12-2. Timer 2 Diagram: Auto-reload Mode (DCEN = 0)

Auto-Reload Mode:

DCEN = 0, T2CM = 00B

Time-out Period

65536

RCAP2H RCAP2L

}

–

Oscillator Frequency

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

TPS

()

Auto-Reload Mode:

DCEN = 0, T2CM = 01B

Time-out Period

RCAP2H RCAP2L

}

Oscillator Frequency

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

TPS

()

÷TPS

TL2

TH2

Reload

Transition

Detector

Timer 2

Interrupt

Overflow

AT89LP428 Arkusz danych(PDF) 56 Page - ATMEL Corporation

AT89LP428 Arkusz danych(HTML) 56 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

Arkusz danych Pobierz

Link URL