HT46R01 datasheet(29/60 Pages) HOLTEK

29 / 60 page

HT46R01/HT46R02/HT46R03

Rev. 1.00

September 21, 2007

A/D Input Pins

All of the A/D analog input pins are pin-shared with the

I/O pins on Port A. Bits PCR0~PCR2 in the ADCR regis-

ter, not configuration options, determine whether the in-

put pins are setup as normal Port A input/output pins or

whether they are setup as analog inputs. In this way,

pins can be changed under program control to change

their function from normal I/O operation to analog inputs

and vice versa. Pull-high resistors, which are setup via

the PAPU register, apply to the input pins only when they

are used as normal I/O pins, if setup as A/D inputs the

pull-high resistors will be automatically disconnected.

Note that it is not necessary to first setup the A/D pin as

an input in the PAC port control register to enable the

A/D input, when the PCR2~PCR0 bits enable an A/D in-

put, the status of the port control register will be overrid-

den. The VDD power supply pin is used as the A/D

converter reference voltage, and as such analog inputs

must not be allowed to exceed this value. Appropriate

measures should also be taken to ensure that the VDD

pin remains as stable and noise free as possible.

Initialising the A/D Converter

The internal A/D converter must be initialised in a spe-

cial way. Each time the A/D channel selection bits are

modified by the program, the A/D converter must be

re-initialised. If the A/D converter is not initialised after

the channel selection bits are changed, the EOCB flag

may have an undefined value, which may produce a

false end of conversion signal. To initialise the A/D con-

verter after the channel selection bits have changed,

then, within a time frame of one to ten instruction cycles,

the START bit in the ADCR register must first be set high

and then immediately cleared to zero. This will ensure

that the EOCB flag is correctly set to a high condition.

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 ADCS0 to ADCS20 in the ACSR

· Step 2

Select which pins on Port A are to be used as A/D in-

puts and configure them as A/D input pins by correctly

programming the PCR0~PCR2 bits in the ADCR reg-

ister.

· Step 3

Select which channel is to be connected to the internal

A/D converter by correctly programming the

ACS0~ACS2 bits which are also contained in the

ADCR register. Note that this step can be combined

with Step 2 into a single ADCR register programming

operation.

· Step 4

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 interrupt control regis-

ter must be set high and the A/D converter interrupt

bit, EADI, in the interrupt control register must also be

set high.

· Step 5

The analog to digital conversion process can now be

initialised by setting the START bit in the ADCR regis-

ter from low to high and then low again. Note that this

bit should have been originally set to a zero value.

· Step 6

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 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 in-

terrupt 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.

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