M3727GM6 Datasheet, PDF (45/129 Pages) Renesas Technology Corp – SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER with CLOSED CAPTION DECODER and ON-SCREEN DISPLAY CONTROLLER

M3727GM6/M8–XXXSP/FP M37272E8SP/FP
8.8 A-D COMPARATOR
A-D comparator consists of 6-bit D-A converter and comparator. A-D
comparator block diagram is shown in Figure 8.8.1.
The reference voltage “Vref” for D-A conversion is set by bits 0 to 5 of
A-D control register 2 (address 00ED16).
The comparison result of the analog input voltage and the reference
voltage “Vref” is stored in bit 4 of A-D control register 1 (address
00EC16).
For A-D comparison, set “0” to corresponding bits of the direction
register to use ports as analog input pins. Write the data for select of
analog input pins to bits 0 to 2 of A-D control register 1 and write the
digital value corresponding to Vref to be compared to the bits 0
to 5 of A-D control register 2. The voltage comparison starts by writ-
ing to A-D control register 2, and it is completed after 16 machine
cycles (NOP instruction ✕ 8).
Data bus
A-D control register 1
Bits 0 to 2
AD1
AD2
Analog
AD3
AD4
signal
AD5
switch
AD6
Comparator control
Compa-
rator
A-D control
register 1
Bit 4
Bit 5
Bit 4
A-D control
register 2
Bit 3
Bit 2
Bit 1
Bit 0
Switch tree
Resistor ladder
Fig. 8.8.1 A-D Comparator Block Diagram
Rev.1.00 Apr 01, 2001 page 45 of 127
REJ03B0132-0100Z