7220 datasheet(88/303 Pages) RENESAS

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2.9 A-D comparator

7220 Group User’s Manual

A-D control register 1

Bits 0 to 2

Comparator control

Data bus

Bit 4

Switch tree

A-D control

Resistor ladder

Compa-

rator

Analog

signal

switch

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

A-D control

P15/A-D1/INT3

P16/A-D2

P17/A-D3

P06/INT2/A-D4

P30/A-D5

P31/A-D6

2.9 A-D comparator

The M37221M6-XXXSP/FP has A-D comparator consists of the 6-bit D-A converter by resistance string

method and a comparator. Figure 2.9.1 shows the A-D comparator block diagram.

Fig. 2.9.1 A-D comparator block diagram

The following explains A-D comparison method.

Set “0” to corresponding bits of the direction register to use ports as analog input pins.

Select the analog input pin with bits 0 to 2 of A-D control register 1 (address 00EE16).

Set the comparison voltage “Vref” for D-A conversion by bits 0 to 5 of A-D control register 2 (address

00EF16). Table 2.9.1 shows the Vref values corresponding to the set values above.

A-D comparison starts by writing to A-D control register 2.

This voltage comparison needs for 16 machine cycles (NOP instruction ! 8).

The comparison result is stored in bit 4 of the A-D control register 1 (address 00EE16).

When the input voltage value is lower than the comparison voltage value, bit 4 is cleared to “0”; when the

input voltage value is higher than the comparison voltage value, bit 4 is set to “1” (refer to “Figure 2.9.2”).

FUNCTIONAL DESCRIPTION

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