7534 datasheet(49/221 Pages) RENESAS

49 / 221 page

HARDWARE

7534 Group

FUNCTIONAL DESCRIPTION

Rev.3.00

Oct 23, 2006

page 36 of 55

REJ09B0178-0300

A/D Converter

The functional blocks of the A/D converter are described below.

[A/D conversion register] AD

The A/D conversion register is a read-only register that stores the

result of A/D conversion. Do not read out this register during an A/D

conversion.

[A/D control register] ADCON

The A/D control register controls the A/D converter. Bit 2 to 0 are

analog input pin selection bits. Bit 4 is the AD conversion completion

bit. The value of this bit remains at “0” during A/D conversion, and

changes to “1” at completion of A/D conversion.

A/D conversion is started by setting this bit to “0” except during an A/

D conversion.

[Comparison voltage generator]

The comparison voltage generator divides the voltage between VSS

and VREF by 1024 by a resistor ladder, and outputs the divided volt-

ages. Since the generator is disconnected from VREF pin and VSS

pin, current is not flowing into the resistor ladder.

[Channel Selector]

The channel selector selects one of ports P27/AN7 to P20/AN0, and

inputs the voltage to the comparator.

[Comparator and control circuit]

The comparator and control circuit compares an analog input volt-

age with the comparison voltage and stores its result into the A/D

conversion register. When A/D conversion is completed, the control

circuit sets the AD conversion completion bit and the AD interrupt

request bit to “1”. Because the comparator is constructed linked to a

capacitor, set f(XIN) to 500 kHz or more during A/D conversion.

Fig. 37 Structure of A/D control register

Fig. 38 Structure of A/D conversion register

Fig. 39 Block diagram of A/D converter

A/D control register

(ADCON : address 003416)

Not used (returns “0” when read)

AD conversion completion bit

0 : Conversion in progress

1 : Conversion completed

Analog input pin selection bits

000 : P20/AN0

001 : P21/AN1

010 : P22/AN2

011 : P23/AN3

100 : P24/AN4

101 : P25/AN5

110 : P26/AN6

111 : P27/AN7

A/D control register

(Address 003416)

A/D control circuit

Resistor ladder

VSS

Comparator

A/D interrupt request

Data bus

P20/AN0

P21/AN1

P22/AN2

P23/AN3

P24/AN4

P25/AN5

P26/AN6

P27/AN7

A/D conversion register (low-order)

(Address 003616)

(Address 003516)

A/D conversion register (high-order)

VREF

Read 8-bit (Read out only address 003516)

(Address 003516)

Read 10-bit (read out in order address 003616, 003516)

(Address 003616)

(Address 003516)

High-order 6-bit of address 003616 returns “0” when read.

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