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STR71x GPIO SCANNING A 4x4 MATRIX KEYPAD

1 HARDWARE LAYOUT

A 4x4 keypad can be very easily interfaced to the STR710’s PORT1 & PORT2 (Figure 1).

Eight lines (P1.0 - 7) are assigned to LED segments. Four lines (P1.8 - 11) are used to drive

and select the 7-segment displays through sink transistors. The same lines are used for

pressed key checking. Keypad rows are connected with pull-down resistors to the four exter-

nal interrupts pins (P2.8 - 11).

Figure 1. Multiplexing matrixed keypad with four 7-segment displays

P1.0

P1.1

P1.2

P1.3

P1.4

P1.5

P1.6

P1.7

P1.8

P1.9

P1.10

P1.11

NPN

NPN

NPN

NPN

4 x 7-segment displays

a

b

c

d

e

f

g

DP

P2.8

P2.9

P2.10

P2.11

LED Module

1

4

7

E

23

A

6

9

0

5

8

C

B

F

D

4x4 KEYPAD

BC 547C

BC 547C

BC 547C

BC 547C

1.2K

1.2K

1.2K

1.2K

0.33K

0.33K

0.33K

0.33K

0.12K

0.12K

0.12K

0.12K

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