mc68hc705p6a Freescale Semiconductor, Inc, mc68hc705p6a Datasheet - Page 53

• Manufacturer Part Number: mc68hc705p6a
• Description: M68hc05 Microcontrollers Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

Chapter 9
Analog Subsystem
9.1 Introduction
The MC68HC705P6A includes a 4-channel, multiplexed input, 8-bit, successive approximation
analog-to-digital (A/D) converter. The A/D subsystem shares its inputs with port C pins PC3–PC7.
9.2 Analog Section
The following paragraphs describe the operation and performance of analog modules within the analog
subsystem.
9.2.1 Ratiometric Conversion
The A/D converter is ratiometric, with pin V
supplying the high reference voltage. Applying an input
REFH
voltage equal to V
produces a conversion result of $FF (full scale). Applying an input voltage equal
REFH
to V
produces a conversion result of $00. An input voltage greater than V
will convert to $FF with
SS
REFH
no overflow indication. For ratiometric conversions, V
should be at the same potential as the supply
REFH
voltage being used by the analog signal being measured and referenced to V
.
SS
9.2.2 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
V
pin internally. V
can be any voltage between V
and V
; however, the accuracy of
SS
REFH
SS
DD
conversions is tested and guaranteed only for V
= V
.
REFH
DD
9.2.3 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.
9.3 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.
9.4 Digital Section
The following paragraphs describe the operation and performance of digital modules within the analog
subsystem.
MC68HC705P6A Advance Information Data Sheet, Rev. 2.1
Freescale Semiconductor
53