AT90PWM3 datasheet(83/361 Pages) ATMEL

83 / 361 page

4317J–AVR–08/10

AT90PWM2/3/2B/3B

Each half period of the external clock applied must be longer than one system clock cycle to

ensure correct sampling. The external clock must be guaranteed to have less than half the sys-

tem clock frequency (f

ExtClk < fclk_I/O/2) given a 50/50% duty cycle. Since the edge detector uses

sampling, the maximum frequency of an external clock it can detect is half the sampling fre-

quency (Nyquist sampling theorem). However, due to variation of the system clock frequency

and duty cycle caused by Oscillator source (crystal, resonator, and capacitors) tolerances, it is

recommended that maximum frequency of an external clock source is less than f

clk_I/O/2.5.

An external clock source can not be prescaled.

Figure 13-2. Prescaler for Timer/Counter0 and Timer/Counter1

(1)

Note:

1. The synchronization logic on the input pins (

Tn/T0) is shown in Figure 13-1.

13.0.4

General Timer/Counter Control Register – GTCCR

• Bit 7 – TSM: Timer/Counter Synchronization Mode

Writing the TSM bit to one activates the Timer/Counter Synchronization mode. In this mode, the

value that is written to the PSRSYNC bit is kept, hence keeping the corresponding prescaler

reset signals asserted. This ensures that the corresponding Timer/Counters are halted and can

be configured to the same value without the risk of one of them advancing during configuration.

When the TSM bit is written to zero, the PSRSYNC bit is cleared by hardware, and the

Timer/Counters start counting simultaneously.

• Bit6 – ICPSEL1:

Timer 1 Input Capture selection

PSRSYNC

Clear

clk

I/O

Synchronization

Bit

543

TSM

ICPSEL1

–

PSRSYNC

GTCCR

Read/Write

R/W

Initial Value

AT90PWM3 датащи(PDF) 83 Page - ATMEL Corporation

AT90PWM3 датащи(HTML) 83 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