AN979 Datasheet, PDF (10/14 Pages) STMicroelectronics – DRIVING AN ANALOG KEYBOARD WITH THE ST7 ADC

DRIVING AN ANALOG KEYBOARD WITH THE ST7 ADC
Figure 7. Flowchart: key detection
KBD_val
no _{EOC = 1?}
yes
disable interrupt
Y = ADCDRL (D1, D0)
A = ADCDRH (D9 - D2)
enable interrupt
X = Offset for Lower
Digital Limit of Key ‘F’
Converted
yes Digital value (A,Y) >= ^no
Specified Lower Digital
limit of Key ‘9’
X = Offset for Lower
Digital Limit of Key ‘8’
Converted
Digital value (A,Y) >= ^no
Specified Lower Digital
+
+
limit of NO_KEY
yes
X = NO_KEY
Reduce the Offset
for Next Lower Key
Converted Digital
no _{value (A,Y) >= Specified}
Lower Digital limit of Key
(pointed by offset)
yes
X = Keyval
return
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