M30620ECFS datasheet(420/621 Pages) RENESAS

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A-D Converter

Mitsubishi microcomputers

M16C / 62 Group

SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER

405

Successive approximation register : n

Vref (V)

–

1024

VREF

2048

VREF

1 to1023

(1) The A-D converter compares the reference voltage (Vref) generated internally based on the

contents of the successive comparison register with the analog input voltage (VIN) input from

the analog input pin. Each bit of the comparison result is stored in the successive comparison

trigger occurs, the A-D converter carries out the following:

1. Fixes bit 9 of the successive comparison register.

Compares Vref with VIN: [In this instance, the contents of the successive comparison

Bit 9 of the successive comparison register varies depending on the comparison re-

sult as follows.

If Vref < VIN, then “1” is assigned to bit 9.

If Vref > VIN, then “0” is assigned to bit 9.

2. Fixes bit 8 of the successive comparison register.

Sets bit 8 of the successive comparison register to “1”, then compares Vref with VIN.

Bit 8 of the successive comparison register varies depending on the comparison

result as follows:

If Vref < VIN, then “1” is assigned to bit 8.

If Vref > VIN, then “0” is assigned to bit 8.

3. Fixes bit 7 through bit 0 of the successive comparison register.

Carries out step 2 above on bit 7 through bit 0.

After bit 0 is fixed, the contents of the successive comparison register (conversion

result) are transmitted to A-D register i.

Vref is generated based on the latest content of the successive comparison register. Table

2.7.10 shows the relationship of the successive comparison register contents and Vref. Table

2.7.11 shows how the successive comparison register and Vref vary while A-D conversion is

in progress. Figure 2.7.23 shows theoretical A-D conversion characteristics.

2.7.11 Method of A-D Conversion (10-bit mode)

Table 2.7.10. Relationship of the successive comparison register contents and Vref

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