HC705P6AGRSSLASHD datasheet(78/134 Pages) NXP

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Analog Subsystem

General Release Specification

MC68HC705P6A — Rev. 1.0

Analog Subsystem

9.3 Analog Section

The following paragraphs describe the operation and performance of

analog modules within the analog subsystem.

9.3.1 Ratiometric Conversion

The A/D converter is ratiometric, with pin VREFH supplying the high

reference voltage. Applying an input voltage equal to VREFH produces a

conversion result of $FF (full scale). Applying an input voltage equal to

VSS produces a conversion result of $00. An input voltage greater than

VREFH will convert to $FF with no overflow indication. For ratiometric

conversions, VREFH should be at the same potential as the supply

voltage being used by the analog signal being measured and referenced

to VSS.

9.3.2 Reference Voltage (V

REFH

)

The reference supply for the A/D converter shares pin PC7 with port C.

The low reference is tied to the VSS pin internally. VREFH can be any

voltage between VSS and VDD; however, the accuracy of conversions is

tested and guaranteed only for VREFH = VDD.

9.3.3 Accuracy and Precision

The 8-bit conversion result is accurate to within

±1 1/2 LSB, including

quantization; however, the accuracy of conversions is tested and

guaranteed only with external oscillator operation.

9.4 Conversion Process

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

converter. Control logic drives the D/A and the analog output is

successively compared to the selected analog input which was sampled

at the beginning of the conversion cycle. The conversion process is

monotonic and has no missing codes.

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

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