MC68HC05PV8 Datasheet, PDF (138/196 Pages) Freescale Semiconductor, Inc – Techinal Data - rev 1.9

Technical Data
Freescale Semiconductor, Inc.
10.2 Introduction
The analog to digital converter system consists of a single 8-bit
successive approximation converter and a channel multiplexer. There is
one 8-bit result data register and one 8-bit status/control register.
The reference supply can be switched by software either to the internal
VDD and VSS supplies or to external pins individually.
An internal RC type oscillator is activated by the ADRC bit in the A/D
status and control register (ADSCR). This RC oscillator is used to
provide a sufficiently high clock rate to the A/D when the bus speed is
too low for the A/D to be accurate.
Additionally, the ADON bit allows the user to save power by
disconnecting the A/D when not in use. This is particularly useful to
reduce current consumption (typically by 100µA) when going into WAIT
mode.
The A/D is ratiometric to the internal reference voltages VREFH and
VREFL which can be derived from either VDD/VSS or external pins. An
input voltage equal to or greater than VREFH converts to $FF (full scale)
with no overflow indication (if greater). An input voltage equal to VREFL
converts to $00. For ratiometric conversions, the source of each analog
input should use VREFH as the supply voltage and be referenced to
VREFL.
10.3 A/D Principle
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 is monotonic
with no missing codes.
Technical Data
MC68HC(8)05PV8/A — Rev. 1.9
Analog to Digital Converter
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