Rainbow-electronics AT90LS4433 Manual do Utilizador descarregar pdf (Página 66)

AT90S/LS4433

1042G–AVR–09/02

keeps running for as long as the ADEN bit is set and is continuously reset when ADEN

is low.

When initiating a conversion by setting the ADSC bit in ADCSR, the conversion starts at

the following rising edge of the ADC clock cycle. The actual sample-and-hold takes

place 1.5 ADC clock cycles after the start of the conversion. The result is ready and writ-

ten to the ADC Result Register after 13 cycles. In Single Conversion mode, the ADC

needs one more clock cycle before a new conversion can be started (see Figure 47). If

ADSC is set high in this period, the ADC will start the new conversion immediately. In

Free Run mode, a new conversion will be started immediately after the result is written

to the ADC Result Register. Using Free Run mode and an ADC clock frequency of 200

kHz gives the lowest conversion time, 65 µs, equivalent to 15.4 kSPS. For a summary of

conversion times, see Table 21.

Figure 46. ADC Timing Diagram, First Conversion (Single Conversion Mode)

MSB of Result

LSB of Result

ADC Clock

ADSC

Hold Strobe

ADIF

ADCH

ADCL

Cycle Number

ADEN

1 212

14 15

16 17

19 20 21 22 23

24 25 26 1

Dummy Conversion Actual Conversion

Second

Conversion

Table 21. ADC Conversion Time

Condition

Sample Cycle

Number

Result

Ready(Cycle Number)

Total Conversion

Time (Cycles)

Total Conversion

Time (µs)

1st Conversion, Free Run 13.5 25 25 125 - 500

1st Conversion, Single 13.5 25 26 130 - 520

Free Run Conversion 1.5 13 13 65 - 260

Single Conversion 1.5 13 14 70 - 280

1 2 ... 61 62 63 64 65 66 67 68 69 70 71 ... 124 125

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