7477 datasheet(272/354 Pages) RENESAS

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

APPLICATION

2.5 A-D converter

7470

7471

7477

7478

(2) Example of A-D conversion setting

An example of A-D conversion setting using the sampling methods

2 + 3 and the determination

method [3] described on the previous page is shown below.

Specifications: After execution of 6-time moving sampling the maximum value and the minimum

value are excluded and then the remaining values are added.

This result is

divided by 4 (times). If the difference from the previous value is less than

±5, the

value is updated. If the same difference is

±5 or more, it is not updated.

Figure 2.5.2 shows an example of control procedure.

,,,,

Fig. 2.5.2 Example of A-D conversion control procedure

(ADRAM)

← AB16

RTS

A816

A916

A616

AB16

A716

A816

Sampling point

A-D conversion result

Minimum

value

Maximum

value

A-D conversion routine

Clear the A-D conversion interrupt

request bit

Set the A-D control register

00 0

!! 11

0 ADCON (Address 00D916)

AD input pin

← P20/IN0

End conversion

VREF is connected (Note 1)

Fixed to “0”

Set the port P20 as an input

After execution of 6-time samplings to this time, the

minimum value and the maximum value are excluded and

then the remaining values are added.

2: Performs this operation only in the 7470/7471

group.

A termination of A-D conversion is verified by the

state of the A-D conversion completion bit, the

state of the A-D conversion completion interrupt

request bit and a branch to the A-D conversion

completion interrupt processing routine.

Wait the VREF stabilizing time

(1.0

µs or more) (Note 2)

Set the A-D control register

!! 10

0 ADCON (Address 00D916)

Clear the A-D conversion

completion bit

Notes 1: The 7477/7478 group is not provided with this bit.

A-D conversion completed ?

(Note 3)

The contents of A-D conversion register is read

and stored into RAM.

A816+A916+A716+A816=2A016

Total of 4-time sampling

2A016

=A816

Compare with the previous fixed

value

Renewal of fixed value

less than

±5

±5 or more

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