HC05V7GRSSLASHD datasheet(79/170 Pages) NXP

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SECTION 10: A/D CONVERTER

Page 65

MC68HC05V7 Specification Rev. 1.0

SECTION 10

A/D CONVERTER

The MC68HC705V7 includes a 16 channel, 8-bit, multiplexed input, successive

approximation A/D converter. When the device is packaged (in a 56-pin SDIP), pin number

restrictions require that 8 channels, AN8 through AN15, are not bonded out.

10.1

ANALOG SECTION

10.1.1

RATIOMETRIC CONVERSION

The A/D is ratiometric, with two dedicated pins supplying the reference voltages (V

REFH

and V

REFL

)

. An input voltage equal to V

REFH converts to $FF (full scale) and an input

voltage equal to V

REFL converts to $00. An input voltage greater than VREFH will convert

to $FF with no overflow indication. For ratiometric conversions, the source of each analog

input should use V

REFH as the supply voltage and be referenced to VREFL.

10.1.2

REFH AND VREFL

The reference supply for the converter uses two dedicated pins rather than being driven by

the system power supply lines because the voltage drops in the bonding wires of those

heavily loaded pins would degrade the accuracy of the A/D conversion. V

REFH and VREFL

can be any voltage between V

SSA1 and VCCA, as long as VREFH > VREFL; however, the

accuracy of conversions is tested and guaranteed only for V

REFL = VSSA1

and V

REFH = VCCA.

10.1.3

ACCURACY AND PRECISION

The 8-bit conversions shall be accurate to within

± 1 1/2 LSB including quantization.

10.2

CONVERSION PROCESS

The A/D reference inputs are applied to a precision internal digital-to-analog converter.

Control logic drives this D/A and the analog output is successively compared to the

selected analog input which was sampled at the beginning of the conversion time. The

conversion process is monotonic and has no missing codes.

10.3

DIGITAL SECTION

10.3.1

CONVERSION TIMES

Each channel of conversion takes 32 clock cycles, which must be at a frequency equal to

or greater than 1 MHz.

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

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