AN979 Datasheet, PDF (4/14 Pages) STMicroelectronics – DRIVING AN ANALOG KEYBOARD WITH THE ST7 ADC

DRIVING AN ANALOG KEYBOARD WITH THE ST7 ADC
Figure 3. Flowchart: conversion process
Conversion Process
KBD_init
no
EOC = 1 ?
yes
read ADCDRL
read ADCDRH
4 ANALOG KEYBOARD
4.1 PRINCIPLE
The purpose is to recognize a key when pressed. In an analog keyboard each key is associ-
ated with a voltage. The description of an analog keyboard is given by Figure 4.
Figure 4. Hardware description of a keyboard with 16 keys
V_DD
R_up
V_key
(Keyboard Value)
R₀
key 0
key 1
R₁
with Σ R_j >> R_up
R₁₃
key 14
R₁₄
key 15
V_SS
R_up is a pull-up resistor. So, when no key is pressed, V_key is equal to V_DD.
4/14