HT46R068B/HT46R069B
Enhanced A/D Type 8-bit OTP MCU
Step 4
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Select which channel is to be connected to the internal A/D converter by correctly programming
the ACS3~ACS0 bits which are also contained in the register.
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, the
INTC0 interrupt control register must be set to “1”, the A/D converter interrupt bit, ADE, must
also be set to “1”.
Step 6
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The analog to digital conversion process can now be initialised by setting the START bit in
the ADCR register from “0” to “1” and then to “0” again. Note that this bit should have been
originally set to “0”.
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.
The setting up and operation of the A/D converter function is fully under the control of the
application program as there are no configuration options associated with the A/D converter. 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 16tAD where tAD is equal to
the A/D clock period.
Programming Considerations
When programming, special attention must be given to the PCR[15:0] bits in the register. If these
bits are all cleared to zero no external pins will be selected for use as A/D input pins allowing the
pins to be used as normal I/O pins. When this happens the internal A/D circuitry will be power
down. Setting the ADONB bit high has the ability to power down the internal A/D circuitry, which
may be an important consideration in power sensitive applications.
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 voltage, this gives a single bit
analog input value of VDD/4096. The diagram show the ideal transfer function between the analog
input value and the digitised output value for the A/D converter.
Note that to reduce the quantisation error, a 0.5 LSB offset is added to the A/D Converter input.
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 level.
Rev. 1.00
ꢄ8
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HOLTEK [ HOLTEK SEMICONDUCTOR INC ]
