68HC05CL48 datasheet(81/145 Pages) MOTOROLA

81 / 145 page

June 6, 1997

GENERAL RELEASE SPECIFICATION

MC68HC05CL48

ANALOG TO DIGITAL CONVERTER

MOTOROLA

REV 2.0

10-1

SECTION 10

ANALOG TO DIGITAL CONVERTER

The MC68HC05CL48 includes a 8-channel, 8-bit, multiplexed input, successive

approximation A/D converter, with four of the input channels available on external

pins and another four internal channels are used for calibration purpose.

10.1

ANALOG SECTION

10.1.1 Ratiometric Conversion

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

(VRH and VRL). An input voltage equal to VRH converts to $FF (full scale) and an

input voltage equal to VRL converts to $00. An input voltage greater than VRH will

convert to $FF with no overﬂow indication. For ratiometric conversions, the source

of each analog input should use VRH as the supply voltage and be referenced to

VRL.

10.1.2 VRH and VRL

RH and VRL are generated internally on chip to reduce pin counts.

10.1.3 Accuracy And Precision

The 8-bit conversions shall be accurate to within

±11/2 LSB including quantization

when averaged over four readings.

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.

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