Rev. 1.50
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HT66F0175/HT66F0185
A/D Flash MCU with EEPROM
HT66F0175/HT66F0185
A/D Flash MCU with EEPROM
A/D Input Pins
All of the A/D analog input pins are pin-shared with the I/O pins as well as other functions. The
corresponding pin-shared function selection bits in the ACERL register determine which external
input pins are selected as A/D converter analog channel inputs or other functional pins. If the
corresponding pin is setup to be an A/D converter analog channel input, the original pin functions
will be disabled. In this way, pins can be changed under program control to change their function
between A/D inputs and other functions. All pull-high resistors, which are setup through register
programming, will be automatically disconnected if the pins are setup as A/D inputs. Note that it
is not necessary to first setup the A/D pin as an input in the port control register to enable the A/D
input as when the relevant A/D input function selection bits enable an A/D input, the status of the
port control register will be overridden.
The A/D converter has its own reference voltage input pin, VREFI. However, the reference voltage
can also be supplied from the power supply pin or an internal Bandgap circuit, a choice which
is made through the SAVRS3~SAVRS0 bits in the SADC2 register. The selected A/D reference
voltage can be output on the VREF pin. The analog input values must not be allowed to exceed the
value of V
REF
. Note that the VREFI or VREF pin function selection bit in the SADC2 register must
be properly configured before the reference voltage pin function is used.
A/D Reference Voltage
The reference voltage supply to the A/D Converter can be supplied from the positive power supply
pin, V
DD
, an external reference source supplied on pin VREFI or an internal reference source derived
from the Bandgap circuit. Then the selected reference voltage source can be amplified through a
programmable gain amplifier except the voltage sourced from V
DD
. The PGA gain can be equal to
1, 2, 3 or 4. The desired selection is made using the SAVRS3~SAVRS0 bits in the SADC2 register
and relevant pin-shared function selection bits. Note that the desired selected reference voltage will
be output on the VREF pin which is pin-shared with other functions. As the VREFI and VREF pins
both are pin-shared with other functions, when the VREFI or VREF pin is selected as the reference
voltage supply pin, the VREFI or VREF pin-shared function selection bit should be properly
configured to disable other pin-shared functions.
A/D Operation
The START bit in the SADC0 register is used to start the AD conversion. When the microcontroller
sets this bit from low to high and then low again, an analog to digital conversion cycle will be
initiated.
The ADBZ bit in the SADC0 register is used to indicate whether the analog to digital conversion
process is in progress or not. This bit will be automatically set to 1 by the microcontroller after an
A/D conversion is successfully initiated. When the A/D conversion is complete, the ADBZ will be
cleared to 0. In addition, the corresponding A/D interrupt request flag will be set in the interrupt
control register, and if the corresponding interrupt control bits are enabled, an 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 poll the ADBZ bit in the SADC0 register to check whether it has been cleared
as an alternative method of detecting the end of an A/D conversion cycle.