7721 datasheet(256/577 Pages) RENESAS

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A-D CONVERTER

7721 Group User’s Manual

12–5

(2)

Trigger select bit (bit 5)

This bit is used to select the source of trigger occurrence. (Refer to section “(3) A-D conversion

start bit.”)

(3)

A-D conversion start bit (bit 6)

q When internal trigger is selected

Setting this bit to “1” generates a trigger, causing the A-D converter to start operating. Clearing

this bit to “0” causes the A-D converter to stop operating.

In the one-shot mode or single sweep mode, this bit is cleared to “0” after the operation is

completed. In the repeat mode or repeat sweep mode, the A-D converter continues operating until

this bit is cleared to “0” by software.

q When external trigger is selected

______

When the ADTRG pin level goes from “H” to “L” with this bit = “1,” a trigger occurs, causing the

A-D converter to start operating. The A-D converter stops when this bit is cleared to “0.”

In the one-shot mode or single sweep mode, this bit remains set to “1” even after the operation

is completed. In the repeat mode or repeat sweep mode, the A-D converter continues operating

until this bit is cleared to “0” by software.

(4)

A-D conversion frequency (

φAD) select bit (bit 7)

As listed in Table 12.2.1, the conversion time of the A-D converter varies depending on the operating

clock (

φAD) selected by this bit.

Since the A-D converter’s comparator consists of capacity coupling amplifiers, keep that

φAD ≥ 250

kHz during A-D conversion.

12.2 Block description

Table 12.2.1 Conversion time per one analog input pin (unit:

µs)

f2/2

28.5

14.25

9.12

f2/4

57.0

28.5

18.24

A-D conversion frequency (

φAD) select bit

φAD

Conversion time

f(XIN) = 8 MHz

f(XIN) = 16 MHz

f(XIN) = 25 MHz

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