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ADP5589CP-EVALZ Datasheet(PDF) 10 Page - Analog Devices

Part No. ADP5589CP-EVALZ
Description  Keypad Decoder and I/O Expansion
Download  52 Pages
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Maker  AD [Analog Devices]
Homepage  http://www.analog.com
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ADP5589CP-EVALZ Datasheet(HTML) 10 Page - Analog Devices

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ADP5589
Data Sheet
Rev. B | Page 10 of 52
KEY
SCAN
CONTROL
1
2
3
4
5
6
7
8
9
VDD
R0
R1
R2
C2
C0
C1
3 × 3 KEYPAD MATRIX
Figure 9. Simplified Key Scan Block
Figure 9 shows a simplified representation of the key scan block
using three row and three column pins connected to a small
3 × 3, nine-switch keypad matrix. When the key scanner is idle,
the row pins are pulled high and the column pins are driven
low. The key scanner operates by checking the row pins to see
if they are low.
If Switch 6 in the matrix is pressed, R1 connects to C2. The key
scan circuit senses that one of the row pins is pulled low, and a
key scan cycle begins. Key scanning involves driving all column
pins high, then driving each column pin, one at a time, low and
sensing whether a row pin is low or not. All row/column pairs are
scanned; therefore, if multiple keys are pressed, they are
detected.
To prevent glitches or narrow press times being registered as a
valid key press, the key scanner requires the key be pressed for
two scan cycles. The key scanner has a wait time between each
scan cycle; therefore, the key must be pressed and held for at
least this wait time to register as being pressed. If the key is
continuously pressed, the key scanner continues to scan, wait,
scan, wait, and so forth.
If Switch 6 is released, the connection between R1 and C2
breaks, and R1 is pulled up high. The key scanner requires that
the key be released for two scan cycles because the release of a
key is not necessarily in sync with the key scanner, it may take
up to two full wait/scan cycles for a key to register as released.
When the key is registered as released, and no other keys are
pressed, the key scanner returns to idle mode.
For the remainder of this document, the press/release status of a
key is represented as simply a logic signal in the figures. A logic
high level represents the key status as pressed, and a logic low
represents released. This eliminates the need to draw individual
row/column signals when describing key events.
KEY x
KEY RELEASED
KEY RELEASED
KEY PRESSED
Figure 10. Logic Low: Released; Logic High: Pressed
Figure 11 shows a detailed representation of the key scan block
and its associated control and status signals. When all row and
column pins are used, a matrix of 88 unique keys can be
scanned.


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