MC68HC705B16CFN Freescale Semiconductor, MC68HC705B16CFN Datasheet - Page 99

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MC68HC705B16CFN

Manufacturer Part Number
MC68HC705B16CFN
Description
IC MCU 2.1MHZ 15K OTP 52-PLCC
Manufacturer
Freescale Semiconductor
Series
HC05r
Datasheet

Specifications of MC68HC705B16CFN

Core Processor
HC05
Core Size
8-Bit
Speed
2.1MHz
Connectivity
SCI
Peripherals
POR, WDT
Number Of I /o
32
Program Memory Size
15KB (15K x 8)
Program Memory Type
OTP
Eeprom Size
256 x 8
Ram Size
352 x 8
Voltage - Supply (vcc/vdd)
4.5 V ~ 5.5 V
Data Converters
A/D 8x8b
Oscillator Type
Internal
Operating Temperature
-40°C ~ 85°C
Package / Case
52-PLCC
Lead Free Status / RoHS Status
Contains lead / RoHS non-compliant

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8
ANALOG TO DIGITAL CONVERTER
The analog to digital converter system consists of a single 8-bit successive approximation
converter and a sixteen channel multiplexer. Eight of the channels are connected to the
PD0/AN0 – PD7/AN7 pins of the MC68HC05B6 and the other eight channels are dedicated to
internal reference points for test functions. The channel input pins do not have any internal output
driver circuitry connected to them because such circuitry would load the analog input signals due
to output buffer leakage current. There is one 8-bit result data register (address $08) and one 8-bit
status/control register (address $09).
The A/D converter is ratiometric and two dedicated pins, VRH and VRL, are used to supply the
reference voltage levels for all analog inputs. These pins are used in preference to the system
power supply lines because any voltage drops in the bonding wires of the heavily loaded supply
pins could degrade the accuracy of the A/D conversion. An input voltage equal to or greater than
8
V
converts to $FF (full scale) with no overflow indication and an input voltage equal to V
RH
RL
converts to $00.
The A/D converter can operate from either the bus clock or an internal RC type oscillator. The
internal RC type oscillator is activated by the ADRC bit in the A/D status/control register (ADSTAT)
and can be used to give a sufficiently high clock rate to the A/D converter when the bus speed is too
low to provide accurate results. When the A/D converter is not being used it can be disconnected,
by clearing the ADON bit in the ADSTAT register, in order to save power (see
Section
8.2.3).
For further information on A/D converter operation please refer to the M68HC11 Reference
Manual — M68HC11RM/AD.
8.1
A/D converter operation
The A/D converter consists of an analog multiplexer, an 8-bit digital to analog converter capacitor
array, a comparator and a successive approximation register (SAR) (see
Figure
8-1).
There are eleven options that can be selected by the multiplexer; AN0–AN7, VRH, (VRH+VRL)/2
or VRL. Selection is done via the CHx bits in the ADSTAT register (see
Section
8.2.3). AN0–AN7
are the only input points for A/D conversion operations; the others are reference points that can
be used for test purposes.
MC68HC05B6
ANALOG TO DIGITAL CONVERTER
Freescale
Rev. 4.1
8-1

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