HT45F23A Datasheet, PDF (79/148 Pages) Holtek Semiconductor Inc – 8-Bit Flash MCU with Op Amps & Comparators

HT45F23A
8-Bit Flash MCU with Op Amps & Comparators
• Step 5
If the interrupts are to be used, the interrupt control registers must be correctly configured to
ensure the A/D converter interrupt function is active. The master interrupt control bit, EMI,
Mulit-function interrupt bit, and the A/D converter interrupt bit, EADI, must all be set high to do
this.
• Step 6
The analog to digital conversion process can now be initialised by setting the START bit in
the ADCR register from low to high and then low again. Note that this bit should have been
originally cleared to zero.
• Step 7
To check when the analog to digital conversion process is complete, the EOCB bit in the ADCR
register can be polled. The conversion process is complete when this bit goes low. When this
occurs the A/D data registers ADRL and ADRH can be read to obtain the conversion value. As an
alternative method, if the interrupts are enabled and the stack is not full, the program can wait for
an A/D interrupt to occur.
Note: When checking for the end of the conversion process, if the method of polling the EOCB bit
in the ADCR register is used, the interrupt enable step above can be omitted.
The accompanying diagram shows graphically the various stages involved in an analog to digital
conversion process and its associated timing. After an A/D conversion process has been initiated
by the application program, the microcontroller internal hardware will begin to carry out the
conversion, during which time the program can continue with other functions. The time taken for the
A/D conversion is 16tADCK where tADCK is equal to the A/D clock period.
Programming Considerations
During microcontroller operations where the A/D converter is not being used, the A/D internal
circuitry can be switched off to reduce power consumption, by setting bit ADONB high in the ACSR
register. When this happens, the internal A/D converter circuits will not consume power irrespective
of what analog voltage is applied to their input lines. If the A/D converter input lines are used as
normal I/Os, then care must be taken as if the input voltage is not at a valid logic level, then this may
lead to some increase in power consumption.
A/D Transfer Function
As the device contain a 12-bit A/D converter, its full-scale converted digitised value is equal to
FFFH. Since the full-scale analog input value is equal to the VDD or VREF voltage, this gives a single
bit analog input value of VDD or VREF divided by 4096.
1 LSB= (VDD or VREF) ÷ 4096
The A/D Converter input voltage value can be calculated using the following equation:
A/D input voltage = A/D output digital value × (VDD or VREF) ÷ 4096
The diagram shows the ideal transfer function between the analog input value and the digitised
output value for the A/D converter. Except for the digitised zero value, the subsequent digitised
values will change at a point 0.5 LSB below where they would change without the offset, and the
last full scale digitised value will change at a point 1.5 LSB below the VDD or VREF level.
Rev. 1.00
79
July 03, 2012