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ST7 KEYPAD DECODING TECHNIQUES, IMPLEMENTING WAKE-UP ON KEYSTROKE

1 ST7 / KEYBOARD INTERFACE

Rows are connected to inputs with pull-up and interrupts (Port C). Columns are connected to

Port A configured as output. The result of the interrupt (the value of the pressed key) is sent on

LEDS (Port B) and stored into the X register. In our configuration, we have to add 4 pull-up re-

sistors on Port A (from PA0 to PA3) to be able to apply a high level on the corresponding pads.

Figure 1. ST7 / keypad interface set-up

ST7

8x560

PC0

PC1

PC2

PC3

PA0

PA1

PA2

PA3

GND

4x100k

2