A/D Conve�Te� Data Registe�S - Adrl� Adrh - Holtek HT66F20-1 Manual

A/D Converter Data Registers – ADRL, ADRH
As the HT66F30-1 or HT66F20-1 device contains an internal 12-bit A/D converter, it requires two
data registers to store the converted value. These are 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 digitised conversion value. As only 12 bits of the
16-bit register space is utilised, the format in which the data is stored is controlled by the ADRFS bit
in the ADCR0 register as shown in the accompanying table. D0~D11 are the A/D conversion result
data bits. Any unused bits will be read as zero.
ADRFS
7
0 D11 D10 D9
1 0
A/D Converter Control Registers – ADCR0, ADCR1, ACERL
To control the function and operation of the A/D converter, three control registers known as ADCR0,
ADCR1 and ACERL are provided. These 8-bit registers define functions such as the selection of
which analog channel is connected to the internal A/D converter, the digitised data format, the
A/D clock source as well as controlling the start function and monitoring the A/D converter end of
conversion status. The ACS2~ACS0 bits in the ADCR0 register and ACS4 bit is the ADCR1 register
define the ADC input channel number. As the devices contain only one actual analog to digital
converter hardware circuit, each of the individual 8 analog inputs must be routed to the converter. It
is the function of the ACS4 and ACS2~ACS0 bits to determine which analog channel input pins or
internal 1.25V is actually connected to the internal A/D converter.
The ACERL control register contains the ACE7~ACE0 bits which determine which pins on Port A
is used as analog inputs for the A/D converter input and which pins are not to be used as the A/D
converter input. Setting the corresponding bit high will select the A/D input function, clearing the
bit to zero will select either the I/O or other pin-shared function. When the pin is selected to be an
A/D input, its original function whether it is an I/O or other pin-shared function will be removed. In
addition, any internal pull-high resistors connected to these pins will be automatically removed if the
pin is selected to be an A/D input.
Rev. 1.40
HT66F20-1/HT66F30-1/HT68F20-1/HT68F30-1
ADRH
6 5 4 3 2 1
D8 D7 D� D5
0 0 0 D11 D10 D9
A/D Data Registers
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Flash MCU with EEPROM
ADRL
0 7 6 5 4 3
D4 D� D� D1 D0 0
D8 D7 D� D5 D4 D�
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2 1 0
0 0 0
D� D1 D0