HT46R01A datasheet(25/58 Pages) HOLTEK

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HT46R01A

Rev. 1.10

August 13, 2008

A/D Converter Data Registers

- ADR

As the device has an 8-bit A/D converter, a single regis-

ter, known as ADR, is used to store the 8-bit analog to

digital conversion value. After the conversion process

takes place, this register can be directly read by the

microcontroller to obtain the digitised conversion value.

In the following tables, D0~D7 are the A/D conversion

data result bits.

Bit7 Bit6 Bit5 Bit4 Bit3 Bit2 Bit1 Bit0

ADR

A/D Data Register

A/D Converter Control Register

- ADCR

To control the function and operation of the A/D con-

verter, a control register known as ADCR is provided.

This 8-bit register defines functions such as the selec-

tion of which analog channel is connected to the internal

A/D converter, which pins are used as analog inputs and

which are used as normal I/Os as well as controlling the

start function and monitoring the A/D converter end of

conversion status.

One section of this register contains the bits

ACS2~ACS0 which define the channel number. As each

of the devices contains only one actual analog to digital

converter circuit, each of the individual 4 analog inputs

must be routed to the converter. It is the function of the

ACS2~ACS0 bits in the ADCR register to determine

which analog channel is actually connected to the inter-

nal A/D converter. Note that the ACS2 bit must always

be assigned a zero value. The ADCR control register

also contains the PCR2~PCR0 bits which determine

which pins on Port A are used as analog inputs for the

A/D converter and which pins are to be used as normal

I/O pins. If the 3-bit address on PCR2~PCR0 has a

value of

²100² or higher, then all four pins, namely AN0,

AN1, AN2 and AN3 will all be set as analog inputs. Note

that if the PCR2~PCR0 bits are all set to zero, then all

the Port B pins will be setup as normal I/Os and the inter-

nal A/D converter circuitry will be powered off to reduce

the power consumption.

The START bit in the ADCR register is used to start and

reset the A/D converter. When the microcontroller sets

this bit from low to high and then low again, an analog to

digital conversion cycle will be initiated. When the

START bit is brought from low to high but not low again,

the EOCB bit in the ADCR register will be set high and

the analog to digital converter will be reset. It is the

START bit that is used to control the overall on/off opera-

tion of the internal analog to digital converter.

The EOCB bit in the ADCR register is used to indicate

when the analog to digital conversion process is com-

plete. This bit will be automatically cleared to zero by the

microcontroller after a conversion cycle has ended. In

addition, the corresponding A/D interrupt request flag

will be set in the interrupt control register, and if the inter-

rupts are enabled, an appropriate internal interrupt sig-

nal will be generated. This A/D internal interrupt signal

will direct the program flow to the associated A/D inter-

nal interrupt address for processing. If the A/D internal

interrupt is disabled, the microcontroller can be used to

poll the EOCB bit in the ADCR register to check whether

it has been cleared as an alternative method of detect-

ing the end of an A/D conversion cycle.

A/D Converter Clock Source Register

- ACSR

The clock source for the A/D converter, which originates

from the system clock fSYS, is first divided by a division

ratio, the value of which is determined by the bits

ADCS0 to ADCS2 in the ACSR register.

Although the A/D clock source is determined by the sys-

tem clock fSYS, and by bits ADCS0 to ADCS2, there are

some limitations on the maximum A/D clock source

speed that can be selected. As the minimum value of

permissible A/D clock period, tAD, is 1us for all devices,

care must be taken for system clock speeds in excess of

1MHz. For system clock speeds in excess of 1MHz, the

ADCS0 to ADCS2 bits should not be set to give an A/D

clock period less than the specified minimum A/D clock

period which may result in inaccurate A/D conversion

values. Refer to the table for examples, where values

marked with an asterisk * show where special care must

be taken, as the values are less than the specified mini-

mum A/D Clock Period.

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