HT56R26 View Datasheet(PDF) - Holtek Semiconductor
Part Name
Description
MFG CO.
'HT56R26' PDF : 134 Pages View PDF
HT56R22/HT56R23/HT56R24/HT56R25/HT56R26
Analog to Digital Converter
The need to interface to real world analog signals is a
common requirement for many electronic systems.
However, to properly process these signals by a
microcontroller, they must first be converted into digital
signals by A/D converters. By integrating the A/D con-
version electronic circuitry into the microcontroller, the
need for external components is reduced significantly
with the corresponding follow-on benefits of lower costs
and reduced component space requirements.
A/D Overview
The device contains an 8-channel analog to digital con-
verter which can directly interface to external analog sig-
nals, such as that from sensors or other control signals
and convert these signals directly into either a 12-bit dig-
ital value.
The accompanying block diagram shows the overall in-
ternal structure of the A/D converter, together with its as-
sociated registers.
A/D Converter Data Registers - ADRL, ADRH
The device, which has an internal 12-bit A/D converter,
requires two data registers, a high byte register, known
as ADRH, and a low byte register, known as ADRL. After
the conversion process takes place, these registers can
be directly read by the microcontroller to obtain the digit-
ised conversion value. Only the high byte register,
ADRH, utilises its full 8-bit contents. The low byte regis-
ter utilises only 4 bit of its 8-bit contents as it contains
only the lowest bits of the 12-bit converted value.
In the following table, D0~D11 is the A/D conversion
data result bits.
Register
Bit
7
Bit
6
Bit
5
Bit
4
Bit
3
Bit
2
Bit
1
Bit
0
ADRL D3 D2 D1 D0 ¾ ¾ ¾ ¾
ADRH D11 D10 D9 D8 D7 D6 D5 D4
A/D Data Registers
A/D Converter Control Registers -
ADCR, ACSR, ADPCR
To control the function and operation of the A/D con-
verter, three control registers known as ADCR, ACSR
and ADPCR are provided. These 8-bit registers define
functions such as the selection of which analog channel
is connected to the internal A/D converter, which pins
are used as analog inputs and which are used as normal
I/Os, the A/D clock source as well as controlling the start
function and monitoring the A/D converter end of con-
version status.
The ACS2~ACS0 bits in the ADCR register define the
channel number. As the device contains only one actual
analog to digital converter circuit, each of the individual
8 analog inputs must be routed to the converter. It is the
function of the ACS2~ACS0 bits in the ADCR register to
determine which analog channel is actually connected
to the internal A/D converter.
The ADPCR control register contains the PCR7~PCR0
bits which determine which pins on PA7~PA0 are used as
analog inputs for the A/D converter and which pins are to
be used as normal I/O pins. If PCR7~PCR0 has a value
of ²11111111², then all eight pins, namely AN7~AN0 will
all be set as analog inputs. Note that if the PCR7~PCR0
bits are all set to zero, then all the PA7~PA0 pins will be
setup as normal I/Os.
A C S R R e g is te r
A D O N B B it
A /D E n a b le
P A 0 /A N 0
P A 1 /A N 1
P A 6 /A N 6
P A 7 /A N 7
fS Y S
C lo c k
D iv id e r
¸N
ADC
ADRL
ADRH
A /D D a ta
R e g is te r s
Rev. 1.30
A D C S 0~A D C S 2
STAR T EO C B
ADCR
R e g is te r
C h a n n e l S e le c t
B its
S ta r t B it E n d o f
C o n v e r s io n B it
A/D Converter Structure
60
December 26, 2014
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