AN980 Datasheet, PDF (2/8 Pages) STMicroelectronics – ST7 KEYPAD DECODING TECHNIQUES

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
V_{DD PC0}
PC1
PC2
PC3
ST7 _PA0
PA1
PA2
PA3
GND
8x560
4x100k
2/8
2