M38041FFHKP datasheet(121/387 Pages) RENESAS

121 / 387 page

1-103

REJ09B0212-0100Z

Rev.1.00

Jan 14, 2005

3804 Group (Spec.H)

HARDWARE

FUNCTIONAL DESCRIPTION SUPPLEMENT

A/D Converter

A/D conversion is started by setting AD conversion completion bit

to “0”. During A/D conversion, internal operations are performed

as follows.

1. After the start of A/D conversion, AD conversion register

goes to “0016”.

2. The highest-order bit of AD conversion register is set to

“1”. and the comparison voltage Vref is input to the

comparator. Then, Vref is compared with analog input voltage

VIN.

3. As a result of comparison, when Vref < VIN, the highest-

order bit of AD conversion register becomes “1.” When

Vref > VIN, the highest-order bit becomes “0.”

By repeating the above operations up to the lowest-order bit of the

AD conversion register, an analog value converts into a digital

value.

In the 10-bit A/D mode, A/D conversion completes at 61 cycles of

2tc(XIN)* (15.25

µs at f(XIN) = 8.0 MHz) after it is started. In the 8-

bit A/D mode, A/D conversion completes at 50 cycles of 2tc(XIN)

(12.5

µs at f(XIN) = 8.0 MHz) after it is started. And the result of

the conversion is stored into the AD conversion register.

Concurrently with the completion of A/D conversion, the A/D con-

version completion bit is set to “1” and an A/D conversion interrupt

request occurs, so that the AD conversion interrupt request bit is

set to “1”.

* tc(XIN) = Main clock input cycle time

When n = 0

Vref = 0

When n = 1 to 1023

Vref =

✕ n

n : Value of A/D converter (decimal numeral)

VREF

1024

✽1–✽10: A result of the first to tenth comparison

Table 22 Change of AD conversion register during A/D conversion (at 10-bit A/D mode)

At start of conversion

First comparison

Second comparison

Third comparison

After completion of

tenth comparison

VREF

✽

Change of AD conversion register

Value of comparison voltage (Vref)

••

•

••

•

••

•

Table 20 Relative formula for a reference voltage VREF of A/D converter and Vref (at 10-bit A/D mode)

000

✽ 11

✽

VREF

••• ±

VREF

1024

A result of A/D conversion

✽ 13

✽✽

✽

✽✽

✽

When n = 0

Vref = 0

When n = 1 to 255

Vref =

✕ (n – 0.5)

n : Value of A/D converter (decimal numeral)

VREF

256

Table 21 Relative formula for a reference voltage VREF of A/D converter and Vref (at 8-bit A/D mode)

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