MC68HC711xxxx Motorola, MC68HC711xxxx Datasheet - Page 63

• Manufacturer Part Number: MC68HC711xxxx
• Description: Microcontrollers
• Manufacturer: Motorola

3.1 Introduction
3.2 Overview
3.2.1 Multiplexer
M68HC11E Family — Rev. 5
MOTOROLA
Data Sheet — M68HC11E Family
The analog-to-digital (A/D) system, a successive approximation converter, uses an
all-capacitive charge redistribution technique to convert analog signals to digital
values.
The A/D system is an 8-channel, 8-bit, multiplexed-input converter. The converter
does not require external sample and hold circuits because of the type of charge
redistribution technique used. A/D converter timing can be synchronized to the
system E clock or to an internal resistor capacitor (RC) oscillator.
The A/D converter system consists of four functional blocks: multiplexer, analog
converter, digital control, and result storage. Refer to
The multiplexer selects one of 16 inputs for conversion. Input selection is controlled
by the value of bits CD:CA in the ADCTL register. The eight port E pins are
fixed-direction analog inputs to the multiplexer, and additional internal analog
signal lines are routed to it.
Port E pins also can be used as digital inputs. Digital reads of port E pins are not
recommended during the sample portion of an A/D conversion cycle, when the
gate signal to the N-channel input gate is on. Because no P-channel devices are
directly connected to either input pins or reference voltage pins, voltages above
V
to maximum ratings. Refer to
input pin.
DD
do not cause a latchup problem, although current should be limited according
Analog-to-Digital (A/D) Converter
Section 3. Analog-to-Digital (A/D) Converter
Figure
3-2, which is a functional diagram of an
Figure
3-1.
Data Sheet
63