HT46R49 Holtek Semiconductor, HT46R49 Datasheet - Page 27

• Manufacturer Part Number: HT46R49
• Description: Cost-Effective A/D Type 8-Bit MCU
• Manufacturer: Holtek Semiconductor

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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
Each of the devices contains a 4-channel analog to digi-
tal converter which can directly interface to external an-
alog signals, such as that from sensors or other control
signals and convert these signals directly into either an
8-bit or 9-bit digital value.
The following diagram shows the overall internal struc-
ture of the A/D converter, together with its associated
registers.
A/D Converter Data Registers - ADR, ADRL, ADRH
For the HT46R46 device, which has an 8-bit A/D con-
verter, a single register, known as ADR, is used to store
the 8-bit analog to digital conversion value. For the re-
maining devices, which have a 9-bit A/D converter, two
registers are required, 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. For devices which use two A/D
Rev. 1.30
HT46R46
HT46R47
HT46R48A
HT46R49
Device
Channels
Input
4
4
4
4
Conversion
Bits
8
9
9
9
Input Pins
PB0~PB3
PB0~PB3
PB0~PB3
PB0~PB3
A/D Converter Structure
HT46R46/C46/R47/C47/R48A/C48A/R49
27
Converter Data Registers, note that only the high byte
register ADRH utilises its full 8-bit contents. The low
byte register utilises only 1 bit of its 8-bit contents as it
contains only the lowest bit of the 9-bit converted value.
In the following tables, D0~D8 are the A/D conversion
data result bits.
A/D Converter Control Register - ADCR
To control the function and operation of the A/D con-
verter, a control register known as ADCR is provided.
This 8-bit register defines functions such as the selec-
tion 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 as well as controlling the
start function and monitoring the A/D converter end of
conversion status.
One section of this register contains the bits
ACS2~ACS0 which define the channel number. As each
of the devices contains only one actual analog to digital
converter circuit, each of the individual 4 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 inter-
nal A/D converter. Note that the ACS2 bit must always
be assigned a zero value.
Register
Register
ADRL
ADRH
ADR
A/D Data Register - Other Devices
A/D Data Register - HT46R46
Bit
D7
Bit
D0
D8
7
7
Bit
D6
Bit
D7
6
6
Bit
D5
Bit
D6
5
5
Bit
D4
Bit
D5
4
4
Bit
D3
Bit
D4
3
3
Bit
D2
Bit
D3
2
2
June 5, 2008
Bit
D1
Bit
D2
1
1
Bit
D0
Bit
D1
0
0