HT56R26 View Datasheet(PDF) - Holtek Semiconductor
Part Name
Description
MFG CO.
'HT56R26' PDF : 134 Pages View PDF
HT56R22/HT56R23/HT56R24/HT56R25/HT56R26
Summary of A/D Conversion Steps
The following summarises the individual steps that
should be executed in order to implement an A/D con-
version process.
· Step 1
Select the required A/D conversion clock by correctly
programming bits ADCS2, ADCS1 and ADCS0 in the
register.
· Step 2
Select which pins are to be used as A/D inputs and
configure them as A/D input pins by correctly program-
ming the PCR7~PCR0 bits in the ADPCR register.
· Step 3
Enable the A/D by clearing the ADONB in the ACSR
register to zero.
· Step 4
Select which channel is to be connected to the internal
A/D converter by correctly programming the
ACS2~ACS0 bits which are also contained in the reg-
ister.
· 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, in the INTC0 interrupt control
register must be set to ²1², the multi-function interrupt
enable bit, EMFI, in the INTC1 register and the A/D
converter interrupt bit, EADI, in the INTC1 register
must also be set to ²1².
· Step 6
The analog to digital conversion process can now be
initialised by setting the START bit in the ADCR regis-
ter from ²0² to ²1² and then to ²0² again. Note that this
bit should have been originally set to ²0².
· Step 7
To check when the analog to digital conversion pro-
cess 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 in-
terrupts are enabled and the stack is not full, the pro-
gram 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 vari-
ous stages involved in an analog to digital conversion
process and its associated timing.
The setting up and operation of the A/D converter func-
tion 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 PCR7~PCR0 bits in the ADPCR register. If these
bits are all cleared to zero no external pins will be se-
lected for use as A/D input pins allowing the pins to be
used as normal I/O pins. 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. The ADONB bit should be set high before
entering any of the low power operating modes or be-
fore a HALT instruction is executed to reduce 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 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 off-
set 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.
A/D Programming Example
The following two programming examples illustrate how
to setup and implement an A/D conversion. In the first
example, the method of polling the EOCB bit in the
ADCR register is used to detect when the conversion
cycle is complete, whereas in the second example, the
A/D interrupt is used to determine when the conversion
is complete.
Rev. 1.30
64
December 26, 2014
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