ATMEGA640 datasheet(157/449 Pages) ATMEL

157 / 449 page

157

ATmega640/1280/1281/2560/2561

2549K–AVR–01/07

The N variable represents the prescaler divider (1, 8, 64, 256, or 1024).

The extreme values for the OCRnx Register represents special cases when generating

a PWM waveform output in the phase correct PWM mode. If the OCRnx is set equal to

BOTTOM the output will be continuously low and if set equal to TOP the output will be

set to high for non-inverted PWM mode. For inverted PWM the output will have the

opposite logic values. If OCR1A is used to define the TOP value (WGM13:0 = 9) and

COM1A1:0 = 1, the OC1A output will toggle with a 50% duty cycle.

Timer/Counter Timing

Diagrams

The Timer/Counter is a synchronous design and the timer clock (clk

Tn) is therefore

shown as a clock enable signal in the following figures. The figures include information

on when Interrupt Flags are set, and when the OCRnx Register is updated with the

OCRnx buffer value (only for modes utilizing double buffering). Figure 57 shows a timing

diagram for the setting of OCFnx.

Figure 57. Timer/Counter Timing Diagram, Setting of OCFnx, no Prescaling

Figure 58 shows the same timing data, but with the prescaler enabled.

Figure 58. Timer/Counter Timing Diagram, Setting of OCFnx, with Prescaler (f

clk_I/O/8)

Figure 59 shows the count sequence close to TOP in various modes. When using phase

and frequency correct PWM mode the OCRnx Register is updated at BOTTOM. The

timing diagrams will be the same, but TOP should be replaced by BOTTOM, TOP-1 by

clk

(clk

I/O/1)

OCFnx

clk

I/O

OCRnx

TCNTn

OCRnx Value

OCRnx - 1

OCRnx

OCRnx + 1

OCRnx + 2

OCFnx

OCRnx

TCNTn

OCRnx Value

OCRnx - 1

OCRnx

OCRnx + 1

OCRnx + 2

clk

I/O

clk

(clk

I/O/8)

ATMEGA640 Datasheet(PDF) 157 Page - ATMEL Corporation

ATMEGA640 Datasheet(HTML) 157 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

Datasheet Download

Link URL