SPMCK16Z4MPV16 datasheet(198/500 Pages) FREESCALE

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ANALOG-TO-DIGITAL CONVERTER

M68HC16 Z SERIES

8-12

USER’S MANUAL

8.7.6 Conversion Timing

Total conversion time is made up of initial sample time, transfer time, final sample time,

and resolution time. Initial sample time is the time during which a selected input chan-

nel is connected to the sample buffer amplifier through a sample capacitor. During

transfer time, the sample capacitor is disconnected from the multiplexer, and the RC

DAC array is driven by the sample buffer amp. During final sampling time, the sample

capacitor and amplifier are bypassed, and the multiplexer input charges the RC DAC

array directly. During resolution time, the voltage in the RC DAC array is converted to

a digital value, and the value is stored in the SAR.

Initial sample time and transfer time are fixed at two ADC clock cycles each. Final sam-

ple time can be 2, 4, 8, or 16 ADC clock cycles, depending on the value of the STS

field in ADCTL0. Resolution time is ten cycles for 8-bit conversion and twelve cycles

for 10-bit conversion.

Transfer and resolution require a minimum of 16 ADC clocks (8

µs with a 2.1 MHz ADC

clock) for 8-bit resolution or 18 ADC clocks (9

µs with a 2.1 MHz ADC clock) for 10-bit

resolution. If maximum final sample time (16 ADC clocks) is used, total conversion

time is 15

µs for an 8-bit conversion or 16 µs for a 10-bit conversion (with a 2.1 MHz

ADC clock).

Figures 8-2 and 8-3 illustrate the timing for 8- and 10-bit conversions, respectively.

These diagrams assume a final sampling period of two ADC clocks.

Figure 8-2 8-Bit Conversion Timing

CYCLE

CYCLES

CYCLE

SAR0

SAR7

SAR6

SAR5

SAR4

SAR3

SAR2

SAR1

CH 8

CH 7

CH 6

CH 5

CH 4

CH 3

CH 2

CH 1

SCF FLAG SET HERE AND SEQUENCE

ENDS IF IN THE 4-CHANNEL MODE

SCF FLAG SET HERE AND SEQUENCE

ENDS IF IN THE 8-CHANNEL MODE

SAMPLE AND TRANSFER

PERIOD

CYCLE

SUCCESSIVE APPROXIMATION

SEQUENCE

END

6 CYCLES

TRANSFER CONVERSION TO

RESULT REGISTER AND SET

CCF

RESOLUTION TIME

INITIAL

SAMPLE

TIME

TRANSFER

TIME

FINAL

SAMPLE

TIME

EOC

16 ADC 8-BIT TIM 1

(2 ADC CLOCKS)

Freescale Semiconductor, Inc.

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SPMCK16Z4MPV16 Datasheet(PDF) 198 Page - Freescale Semiconductor, Inc

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