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Standard 8051 8-Bit Flash MCU
HT85F2260/HT85F2270/HT85F2280
Analog to Digital Converter –
ADC
Analog to Digital Converter –
ADC
ADPGA Register
SFR Address: F4h
Bit
7
6
5
4
3
2
1
0
Name
—
—
—
—
—
ADGN�
ADGN1
ADGN0
R/W
—
—
—
—
—
R/W
R/W
R/W
POR
—
—
—
—
—
0
0
0
Bit 7~3
Unimplemented, read as “0”
Bit 2~0
ADGN2~ADGN0:
PGA gain select
000: PGA off
001: 0.5
010: 1
011: 2
100: 4
101: 8
110: 12
111: 16
These three bits are used to select the PGA internal gain setting to allow greater A/D
Converter input voltage dynamic range.
A/D Operation
Controlling the power on/off function of the A/D converter circuitry is implemented using the
ADOFF bit in the ADCR0 register. This bit must be zero to power on the A/D converter. When the
ADOFF bit is cleared to zero to power on the A/D converter internal circuitry a certain delay, as
indicated in the timing diagram, must be allowed before an A/D conversion is initiated. Even if no
pins are selected for use as A/D inputs by clearing the ACE7~ACE0 bits in the ADCR2 register, if
the ADOFF bit is zero then some power will still be consumed. In power conscious applications it
is therefore recommended that the ADOFF is set high to reduce power consumption when the A/D
converter function is not being used.
The reference voltage supply to the A/D Converter can be supplied from either the positive power
supply pin, VCCA3, internal voltage reference or from an external reference sources supplied on
pin VREF. The desired selection is made using the VREFAS and VREFIS bits.
The START bit in the ADCR0 register is used to start and reset the A/D converter. When the
microcontroller sets this bit from low to high and then low again, an analog to digital conversion
cycle will be initiated. When the START bit is brought from low to high but not low again, the
EOCB bit in the ADCR0 register will be set high and the analog to digital converter will be reset.
It is the START bit that is used to control the overall start operation of the internal analog to digital
converter.
The EOCB bit in the ADCR0 register is used to indicate when the analog to digital conversion
process is complete. This bit will be automatically set to “0” by the microcontroller after a
conversion cycle has ended. In addition, the corresponding A/D interrupt request flag will be set
in the interrupt control register, and if the interrupts are enabled, an appropriate internal interrupt
signal will be generated. This A/D internal interrupt signal will direct the program flow to the
associated A/D internal interrupt address for processing. If the A/D internal interrupt is disabled,
the microcontroller can be used to poll the EOCB bit in the ADCR0 register to check whether it has
been cleared as an alternative method of detecting the end of an A/D conversion cycle.