Rev. 1.21
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HT66F488/HT66F489
A/D Flash MCU with EEPROM
HT66F488/HT66F489
A/D Flash MCU with EEPROM
A/D Converter Data Registers – ADRL, ADRH
As the 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
ADRH
ADRL
7
6
5
4
3
2
1
0
7
6
5
4
3
2
1
0
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D11 D1� D� D8 D�
D6 D5 D4 D3 D2 D1 D�
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1
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D11 D1� D� D8 D� D6 D5 D4 D3 D2 D1 D�
A/D Data Registers
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, 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 ACS4 in the ADCR1 register and ACS2~ACS0 bits in the ADCR0 register
define the ADC input channel number. As the device contains 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, ACS2 ~ ACS0 bits to determine which analog channel input signals or
internal V
BG
is actually connected to the internal A/D converter.
The ACERL control register contains the ACE7~ACE0 bits which determine which pins on Port C
are 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.