7906 datasheet(302/531 Pages) RENESAS

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A-D CONVERTER

7906 Group User’s Manual Rev.2.0

12-7

12.2 Block description

(1)

Analog input pin select bits (bits 0 to 2 at address 1E16)

These bits are used to select an analog input pin in the one-shot mode or repeat mode. Pins which

are not selected as analog input pins serve as programmable I/O port pins.

Also, these bits must be specified again if the user switches the operation mode to the one-shot

mode or repeat mode after the operation is performed in the single sweep mode or repeat sweep

mode 0.

(2)

A-D operation mode select bits (bits 3 and 4 at address 1E16)

These bits are used to select the operation mode of the A-D converter.

(3)

A-D conversion start bit (bit 6 at address 1E16)

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

this bit to “0” causes the A-D converter to halt its operation.

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

In the repeat mode or repeat sweep mode 0, the A-D converter continues its operation until this bit

is cleared to “0” by software.

(4) A-D conversion frequency (

φAD) select bit 0 (bit 7 at address 1E16), A-D conversion frequency

(

φAD) select bit 1 (bit 4 at address 1F16)

These bits are used to select the operation clock (

φAD) of the A-D converter. Table 12.2.1 lists the

conversion time per one analog input pin.

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

φAD ≥ 250 kHz while the A-D converter is active.

(5)

A-D sweep pin select bits (bits 0 and 1 at address 1F16)

These bits are used to select analog input pins in the single sweep mode or repeat sweep mode 0.

Pins which are not selected as analog input pins serve as programmable I/O port pins or as I/O pins

of other internal peripheral devices, which are multiplexed.

(6)

Resolution select bit (bit 3 at address 1F16)

This bit is used to select a resolution.

(7)

VREF connection select bit (bit 6 at address 1F16)

When the A-D converter is not used, this bit is used to disconnect the resistor ladder network of the

A-D converter from the reference voltage input pin (VREF).

When the resistor ladder network is disconnected from pin VREF, the current is not flowed from pin

VREF to resistor ladder network. Accordingly, the power dissipation can be saved.

When this bit changes from “1” (VREF disconnected) to “0” (VREF connected), start of the operation

must be 1

µs or more later.

8-bit resolution

mode

10-bit resolution

mode

fsys = 20 MHz

Conversion time (

µs) (Note)

φAD

f2 divided by 4

f2 divided by 2

19.60

9.80

4.90

2.45

A-D conversion

frequency (

φAD)

select bit 1

A-D conversion

frequency (

φAD)

select bit 0

23.60

11.80

5.90

Comparator

function

Do not select.

5.60

2.80

1.40

0.70

Note: This applies when the peripheral devices’ clock select bits 0, 1 (bits 6, 7 at address BC16) = “002.”

Table 12.2.1 Conversion time per one analog input pin

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