HT48R02N datasheet(45/71 Pages) HOLTEK

45 / 71 page

HT46R01B/02B/01N/02N

HT48R01B/02B/01N/02N

Rev.1.10

February 12, 2010

The ADCR control register also contains the

PCR3~PCR0 bits which determine which pins on

PA0~PA3 are used as analog inputs for the A/D converter

and which pins are to be used as normal I/O pins. Note

that if the PCR3~PCR0 bits are all set to zero, then all the

PA0~PA3 pins will be setup as normal I/Os.

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

the A/D converter. When themicrocontroller 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 to a

²1² and the analog

to digital converter will be reset. It is the START bit that is

used to control the overall start operation 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 set to

²0² 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.

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 ADCS2,

ADCS1 and ADCS0 bits in the ACSR register.

The A/D converter overall on/off control is a function of

both the ADONB bit in the ACSR register and the PCRn

bits in the ADCR register as shown in the table. Either

the ADONB bit cleared to zero or the PCRn bits set to a

zero value will switch off the A/D converter. These are

important consideration in power sensitive applications

and must be taken into account if power consumption is

to be minimised. As the table illustrates, execution of the

HALT instruction has no effect on the A/D converter

on/off control and subsequently its power consumption.

PCRn

Bits

HALT

Instruction

ADONB

Bit

ADC

On/Off

= 0

Off

> 0

Off

Note: X: Don

¢t care

A/D Converter On/Off Control

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

tem clock fSYS, and by bits ADCS2, ADCS1 and ADCS0,

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,is0.5

ms, care must be

taken for system clock speeds equal to or greater than

4MHz. For example, the system clock operates at a fre-

quency of 4MHz, the ADCS2, ADCS1 and ADCS0 bits

should not be set to

²100². Doing so will give A/D clock pe-

riods that are less than the minimum A/D clock period

which may result in inaccurate A/D conversion values. Re-

fer to the following table for examples, where values

marked with an asterisk * show where, depending upon

the device, special care must be taken, as the values may

be less than the specified minimum A/D Clock Period.

· ACSR Register

Bit

76543210

Name

TEST

ADONB

¾¾¾

ADCS2

ADCS1

ADCS0

R/W

¾¾¾

R/W

POR

¾¾¾

000

Bit 7

TEST: for test mode use only

Bit 6

ADONB: ADC module power on/off control bit

0: ADC module power on

1: ADC module power off

Note: 1. it is recommended to set ADONB=1 before entering sleep for saving power.

2. ADONB=1 will power down the ADC module.

Bit 5~3

unimplemented, read as

²0²

Bit 2~0

ADCS2~ADCS0 : Select A/D converter clock source

000: system clock/2

001: system clock/8

010: system clock/32

011: undefined, can

¢t be used.

100: system clock

101: system clock/4

110: system clock/16

111: undefined, can

¢t be used.

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