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When the key on line being scanned is pressed and the contact is closed,
the current passes from the pull-up register, through the diode of the key
being pressed, to the scan driver.
This drops the potential of the Y-axis
data bits (DBO-DB7 of the microprocessor) corresponding to the key, thus
determining which key is being pressed.
Y
___
of
oN
scan
————
A
]
~
{C_
rT
Driver
D
(\
t
(¢
ay
Micro-
pro-
cessor
DB/7
Figure 4-12
Scanning
As Figure 4-12 shows, when key A is pressed and line @)
on the X-axis is
scanned, the line
(2) on the Y-axis goes low.
The microprocessor then
detects that scanning lines @)
and
(2) are low, and determines key A is
being pressed.
Iv - 13
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Troubleshooting
