7477 datasheet(159/354 Pages) RENESAS

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7470/7471/7477/7478 GROUP USER’S MANUAL

1-142

HARDWARE

1.14 A-D converter

2 Conversion time

q After a start of A-D conversion, this A-D conversion terminates after 50 cycles (12.5

µs at f(XIN)

= 8 MHz).

q Main clock input oscillation frequency f(XIN)/2 is used as an operating clock for the A-D converter,

so the A-D conversion time can be basically obtained by the following expression.

A-D conversion time =

f(XIN)

× conversion cycle (50: cycles)

Note: Because the comparator is configurated by capacity coupling, use the A-D converter in the

following condition.

f(XIN)

> 1 MHz

Accordingly, use the A-D converter in the condition that bit 7 of the CPU mode register

(address 00FB16) is “0” (ordinary mode).

[Setting method]

In the 7470/7471 group

1 Clear the bit of the Port P2 direction register corresponding to the used analog input pin to “0”

(input mode).

2 Clear the port pull-up control bit corresponding to the used analog input pin to “0” (no pull-up).

3 Clear the A-D conversion interrupt request bit of the Interrupt request register 1 to “0.”

Note: After A-D conversion is started, the A-D conversion interrupt request bit is not cleared to “0”

automatically.

4 When using an A-D conversion interrupt, set the A-D conversion interrupt enable bit to “1” to

provide an interrupt enable state.

5 Set the A-D control register as follows.

q Select an analog input pin by the analog input pin selection bit.

q Set the VREF connection selection bit to “1” and connect VREF to a ladder resistor.

6 Wait for 1.0 µs or more as VREF stabilizing time.

7 Clear the A-D conversion end bit of the A-D control register to “0.” (With this setting, A-D conversion

is started.)

In the 7477/7478 group

1 Clear the A-D conversion interrupt request bit of the Interrupt request register 1 to “0.”

Note: After A-D conversion is started, the A-D conversion interrupt request bit is not cleared to “0”

automatically.

2 When using an A-D conversion interrupt, set the A-D conversion interrupt enable bit to “1” to

provide an interrupt enable state.

3 Set the A-D control register as follows.

q Select an analog input pin by the analog input pin selection bit.

q Clear the A-D conversion end bit to “0.” (With this setting, A-D conversion is started.)

Don't read the contents of the A-D conversion register during A-D conversion.

For register setting, refer to “Table 1.14.1 Setting at A-D Conversion.”

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