HT45F23 datasheet(78/152 Pages) HOLTEK

78 / 152 page

fSYS

A/D Clock Period (tADCK)

ADCS2,

ADCS1,

ADCS0

= 100

(fSYS)

ADCS2,

ADCS1,

ADCS0

= 000

(fSYS/2)

ADCS2,

ADCS1,

ADCS0

= 101

(fSYS/4)

ADCS2,

ADCS1,

ADCS0

= 001

(fSYS/8)

ADCS2,

ADCS1,

ADCS0

=110

(fSYS/16)

ADCS2,

ADCS1,

ADCS0

= 010

(fSYS/32)

ADCS2,

ADCS1,

ADCS0

= 111

=011

1MHz

ms2ms4ms8ms16ms32ms

Undefined

2MHz

500ns

ms2ms4ms8ms16ms

Undefined

4MHz

250ns*

500ns

ms2ms4ms8ms

Undefined

8MHz

125ns*

250ns*

500ns

ms2ms4ms

Undefined

12MHz

83ns*

167ns*

333ns*

667ns

1.33

2.67

Undefined

A/D Clock Period Examples

Controlling the power on/off function of the A/D converter circuitry is implemented using the

ADONB bit in the ACSR register. This bit must be zero to power on the A/D converter. When the

ADONB bit is cleared to zero to power on the A/D converter internal circuitry a certain delay, as

indicated in the timing diagram, must be allowed before an A/D conversion is initiated. Even if no pins

are selected for use as A/D inputs by clearing the PCR5~PCR0 bits in the ADPCR register, if the

ADONB bit is zero then some power will still be consumed. In power conscious applications it is

therefore recommended that the ADONB is set high to reduce power consumption when the A/D

converter function is not being used.

The reference voltage supply to the A/D Converter can be supplied from either the positive power

supply pin, VDD, or from an external reference sources supplied on pin VREF. The desired selection is

made using the VRSEL bit. As the VREF pin is pin-shared with other functions, when the VRSEL bit

is set high, the VREF pin function will be selected and the other pin functions will be disabled

automatically.

A/D Input Pins

The A/D analog input pins are pin-shared with the I/O pins on Port B and Port C as well as other

functions. The PCR5~ PCR0 bits in the ADPCR register, determine whether the input pins are setup as

A/D converter analog inputs or whether they have other functions. If the PCR5~ PCR0 bits for its

corresponding pin is set high then the pin will be setup to be an A/D converter input and the original

pin functions disabled. In this way, pins can be changed under program control to change their function

between A/D inputs and other functions. All pull-high resistors, which are setup through register

programming, will be automatically disconnected if the pins are setup as A/D inputs. Note that it is not

necessary to first setup the A/D pin as an input in the PBC or PCC port control register to enable the

A/D input as when the PCR5~ PCR0 bits enable an A/D input, the status of the port control register

will be overridden.

Rev. 1.20

September 15, 2011

HT45F23/HT45F43

8-Bit Flash MCU with Op Amps & Comparators

A N 0

A N 5

P C 4 / V R E F

V D D

V R S E L

V R E F

1 2 - b i t A D C

I n p u t V o l t a g e

A C S 2 ~

A C S 0

O P A 1 o u t p u t

O P A 2 o u t p u t

A/D Input Structure

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