Advanced Assembly Programming - The HCS12/9S12: An Introduction to Software and Hardware Interfacing - page 191

HCS12

470 Ω each

a

a
b
c
d
e
f
g
common cathode

PB6
PB5
PB4
PB3
PB2
PB1
PB0

f

b

g

e c

d

Figure 4.17 ■ Driving a single seven-segment display

Decimal
Digit

Segments Corresponding Hex Number

a b c d e f g Figure 4.17 Circuit Dragon12 Demo Board

0 1 1 1 1 1 1 0 $7E $3F

1 0 1 1 0 0 0 0 $30 $06

2 1 1 0 1 1 0 1 $6D $5B

3 1 1 1 1 0 0 1 $79 $4F

4 0 1 1 0 0 1 1 $33 $66

5 1 0 1 1 0 1 1 $5B $6D

6 1 0 1 1 1 1 1 $5F $7D

7 1 1 1 0 0 0 0 $70 $07

8 1 1 1 1 1 1 1 $7F $7F

9 1 1 1 1 0 1 1 $7B $6F

Table 4.7 ■ Decimal to seven-segment decoder

The circuit in Figure 4.18 can display up to six digits by utilizing the time-multiplexing
technique, in which each seven-segment display is lighted in turn briefly and then turned off.
When one display is lighted, all other displays are turned off. Within one second, each seven-
segment display is lighted and then turned off many times. Because of the persistence of vision ,
all six displays will appear to be lighted simultaneously.

Example 4.13
▼

Write an instruction sequence to display 7 on the seven-segment display #5 in Figure 4.18.
Solution: To display 7 on display #5, we need to
• Output the hex value $07 to Port B
• Set the PP5 pin to low
• Set pins PP4 through PP0 to high