7721 datasheet(456/577 Pages) RENESAS

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APPLICATION

7721 Group User’s Manual

16–53

16.2 Examples of using DMA controller

16.2.3 Example of dynamic lighting for LED

The following is an example of dynamic lighting for LED by using DMA3 and Timer B0.

(1)

Specifications

•The eight 7-segment LEDs are lighted up; port P6 outputs the segment data; port P7 outputs the

digit data. (Refer to “Figure 16.2.11.”)

•The display data and the segment data are transferred from the data buffer to the port P6 and P7

registers by DMA3.

•Digit switch interval is generated by Timer B0.

•16 bytes of RAM are used as the data buffer. 1-digit display data consists of 2 bytes; the digit data

is placed in the high-order byte; the segment data is placed in the low-order byte. (Refer to “Table

16.2.2.”)

When the digit data and segment data are “0,” the LED is lighted up (ON): when they are “1,” the

light goes out (OFF).

Assuming that the segment pattern is generated by another processing.

M37721

LED

driver

Data buffer

P67

P60

P77

P70

7-segment LED ! 8

LED

driver

Data buffer

Digit data

00000001

00000010

00000100

00001000

00010000

00100000

01000000

10000000

Segment pattern of the

contents to be displayed

in each digit

Segment pattern

Fig. 16.2.11 Example of dynamic lighting for LED

Table 16.2.2 Data buffer

Notes 1: This applies in the following:

•when the digit data is “0,” the light goes

out.

•when the digit data is “1,” the LED is lighted

up.

2: Assuming that the segment pattern is

generated by another processing.

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