7477 datasheet(23/48 Pages) RENESAS

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MITSUBISHI MICROCOMPUTERS

7477/ 7478 GROUP

SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER

A-D CONVERTER

The A-D conversion uses an 8-bit successive comparison method.

Figure 13 shows a block diagram of the A-D conversion circuit.

Conversion is automatically carried out once started by the pro-

gram.

There are eight analog input pins which are shared with P20 to

P27 of port P2 (Only P20 to P23 4-bit for 7477 group).

Which analog inputs are to be A-D converted is specified by using

bit 2 to bit 0 in the A-D control register (address 00D916). Pins for

inputs to be A-D converted must be set for input by setting the di-

rection register bit to “0”. Bit 3 in the A-D control register is an A-D

conversion end bit. This is “0” during A-D conversion; it is set to “1“

when the conversion is terminated. Therefore, it is possible to

know whether A-D conversion is terminated by checking this bit.

Figure 14 shows the relationship between the contents of A-D

control register and the selected input pins.

Fig. 13 A-D converter circuit

The A-D conversion register (address 00DA16) contains informa-

tion on the results of conversion, so that it is possible to know the

results of conversion by reading the contents of this register.

The following explains the procedure to execute A-D conversion.

First, set values to bit 2 to bit 0 in the A-D control register to select

the pins that you want to execute A-D conversion. Next, clear the

A-D conversion end bit to “0”. When the above is done, A-D con-

version is initiated. The A-D conversion is completed after an

elapse of 50 machine cycles (12.5

µs when f(XIN) = 8MHz), the A-

D conversion end bit is set to “1”, and the interrupt request bit is

set to “1”. The results of conversion are contained in the A-D con-

version register.

Comparator

A-D control circuit

Switch tree

Ladder resistor

A-D conversion

completion

interrupt request

VSS (Note 1)

VREF

1 : AVSS for M37478M4/M8/E8-XXXFP and M37478M2/M4/M8/E8TXXXFP.

2 : The 7477 group does not have P2 4/IN4 to P27/IN7 pins.

P20/IN0

P21/IN1

P22/IN2

P23/IN3

P24/IN4

P25/IN5

P26/IN6

P27/IN7

Data bus

A-D control register

(address 00D916)

bit 3

Notes

bit 0

A-D conversion register

(address 00DA16)

7477 Datasheet(PDF) 23 Page - Renesas Technology Corp

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