M38264EBFS datasheet(38/91 Pages) RENESAS

38 / 91 page

Rev.1.00

Sep 06, 2006

page 38 of 88

REJ03B0181-0100

3826 Group (One Time PROM version)

A/D CONVERTER

[AD Conversion Low-Order Register (ADL)]

001416

[AD Conversion High-Order Register (ADH)]

003516

The AD conversion registers are read-only registers that store the

result of an A/D conversion. When reading this register during an

A/D conversion, the previous conversion result is read.

The high-order 8 bits of a conversion result is stored in the AD

conversion high-order register (address 003516), and the low-or-

der 2 bits of the same result are stored in bit 7 and bit 6 of the AD

conversion low-order register (address 001416).

Bit 0 of the AD conversion low-order register is the conversion

mode selection bit. When this bit is set to “0”, that becomes the

10-bit A/D mode. When this bit is set to “1”, that becomes the 8-bit

A/D mode.

[AD Control Register (ADCON)] 003416

The AD control register controls the A/D conversion process. Bits

0 to 2 of this register select specific analog input pins. Bit 3 indi-

cates the completion of an A/D conversion. The value of this bit re-

mains at “0” during an A/D conversion, then it is set to “1” when

the A/D conversion is completed. Writing “0” to this bit starts the

A/D conversion.

Bit 4 is the VREF input switch bit which controls connection of the

resistor ladder and the reference voltage input pin (VREF). The

resistor ladder is always connected to VREF when bit 4 is set to

“1”. When bit 4 is set to “0”, the resistor ladder is cut off from VREF

except for A/D conversion performed. When bit 5, which is the AD

external trigger valid bit, is set to “1”, A/D conversion starts also by

a falling edge of an ADT input. When using an A/D external trigger,

set the P57/ADT pin to input mode (set “0” to bit 7 of port P5 direc-

tion register).

Comparison Voltage Generator

The comparison voltage generator divides the voltage between

AVSS and VREF by 256 (when 8-bit A/D mode) or 1024 (when 10-

bit A/D mode), and outputs the divided voltages.

Channel Selector

The channel selector selects one of the input ports P67/AN7–P60/AN0.

Comparator and Control Circuit

The comparator and control circuit compare an analog input volt-

age with the comparison voltage and store the result in the AD

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

control circuit sets the AD conversion completion bit and the A/D

conversion interrupt request bit to “1”.

Note that because the comparator consists of a capacitor

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

Use the clock divided from the main clock f(XIN) as the system clock

φ.

Fig. 38 Structure of A/D converter-related registers

AD control register

(ADCON : address 003416)

AD conversion completion bit

0 : Conversion in progress

1 : Conversion completed

Analog input pin selection bits

b2b1b0

0 0 0 : P60/AN0

0 0 1 : P61/AN1

0 1 0 : P62/AN2

0 1 1 : P63/AN3

1 0 0 : P64/AN4

1 0 1 : P65/AN5

1 1 0 : P66/AN6

1 1 1 : P67/AN7

VREF input switch bit

0 : AUTO

1 : ON

AD external trigger valid bit

0 : A/D external trigger invalid

1 : A/D external trigger valid

Interrupt source selection bit

0 : Interrupt request at AD

conversion completed

1 : Interrupt request at ADT

input falling

Not used (“0” at reading)

AD conversion low-order register

(ADL : address 001416)

Conversion mode selection bit

0 : 10-bit A/D mode

1 : 8-bit A/D mode

Not used (“0” at reading)

•For 10-bit A/D mode

A/D conversion result

•For 8-bit A/D mode

Not used (undefined at reading)

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