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ADP5587ACPZ-R7 Datasheet(PDF) 9 Page - Analog Devices

Part No. ADP5587ACPZ-R7
Description  Mobile I/O Expander and QWERTY Keypad Controller
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Maker  AD [Analog Devices]
Homepage  http://www.analog.com
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ADP5587ACPZ-R7 Datasheet(HTML) 9 Page - Analog Devices

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ADP5587
Rev. B | Page 9 of 24
To prevent glitches or narrow press times registering as valid
key presses, the key scanner requires the key to be pressed for
two scan cycles. The key scanner has a sampling period of 25 ms;
therefore, the key must be pressed and held for at least 25 ms to
register as pressed. If the key is continuously pressed, the key
scanner continues to sample every 25 ms. If a pressed key is
released for 25 ms or greater, the state machine sets the
appropriate key number in the key event status register with the
key-pressed bits cleared in the order detected. Because the
release of a key is not necessarily in sync with the key scan
sampling period, it may take between 25 ms and 50 ms for a key
to register as released. After the key is registered as released, the
key scanner returns to idle mode. Figure 10 shows the row and
column pins connected to a typical 10 × 8, 80-switch keypad
matrix.
J7
I7
H7
G7
F7
E7
D7
C7
B7
A7
J6
I6
H6
G6
F6
E6
D6
C6
B6
A6
J5
I5
H5
G5
F5
E5
D5
C5
B5
A5
J4
I4
H4
G4
F4
E4
D4
C4
B4
A4
J3
I3
H3
G3
F3
E3
D3
C3
B3
A3
J2
I2
H2
G2
F2
E2
D2
C2
B2
A2
J1
I1
H1
G1
F1
E1
D1
C1
B1
A1
J0
I0
H0
G0
F0
E0
D0
C0
B0
A0
R7 R6 R5 R4 R3 R2 R1 R0
C0 C1 C2 C3 C4 C5 C6 C7
C9
C8
10 × 8 KEYPAD MATRIX
VCC
NOTES:
1. Dx_PULL STANDS FOR GPIO PULL-UP.
Figure 10. Keypad Decode Configuration
Key Event Tracking
The 10 key event registers are set to act as a FIFO, meaning that
reading any of the 10 key event registers yields the key events in
the order the keys were pressed and released.
Tracking of key events is done with the help of the key event
counter (the KEC field in Register 0x03) and the FIFO/key
event registers (Register 0x04 through Register 0x0D). The KEC
count increases as keys are pressed and released; up to 10 events
can be logged in the counter. The FIFO/key event registers, on
the other hand, display the key events and their status (pressed
or released) as they are read out of the FIFO. The FIFO registers
contain eight bits, with the MSB dedicated as the status bit (1
indicates a press and 0 indicates a release); the remaining seven
bits display the binary representation of the keys that are pressed
or released.
The first read of any of the FIFO registers displays the first
event that happened and its status. Subsequent reads of the
same register replace the register data with the next event that
happens. If tracking of all the events is important, it is best to
use a single register per event. After all the events in the FIFO
are read, reading of any of the event registers yields a zero value.
Table 10 and Table 11 show the event sequences as they are
logged in and read from the FIFO. The 10 FIFO registers are
labeled A through J, and the keys are labeled A0 through J7.
Table 10. Example of Event Sequence
Key Pressed/Released
Status
Key Event Counter
A0
Pressed
1
B1
Pressed
2
A0
Released
3
C2
Pressed
4
B1
Released
5
D3
Pressed
6
C2
Released
7
E4
Pressed
8
E4
Released
9
D3
Released
10
Table 11. Interpretation of FIFO Event Reading
Key Event
Counter
Key Event
Register
Read
Key Event Reg-
ister Content
(Binary)1
Key Event
Register
Interpretation
10
N/A
N/A
N/A
9
D
1 0000000
Key A0 pressed
8
E
1 0001100
Key B1 pressed
7
C
0 0000000
Key A0 released
6
F
1 0010111
Key C2 pressed
5
G
0 0001100
Key B1 released
4
A
1 0100010
Key D3 pressed
3
B
0 0010111
Key C2 released
2
H
1 0101101
Key E4 pressed
1
J
0 0101101
Key E4 released
0
I
0 0100010
Key D3 released
1
The MSB indicates a key press or key release in the key event register: 1 = key
press; 0 = key release.
Key Event Overflow
The ADP5587 is equipped with an overflow feature to handle
key events beyond the FIFO capacity. When all events are filled, any
additional events set the OVR_FLOW_INT bit in Register 0x02;
if the OVR_FLOW_IEN bit in Register 0x01 is set, the host
processor is also interrupted when overflow occurs. When the
FIFO is not full, new events are added as the last events.
The OVR_FLOW_M bit in Register 0x01 sets the mode of
operation during overflows. Clearing the OVR_FLOW_M bit
causes new incoming events to be discarded, and setting this bit
rolls over and overwrites old data with new data starting at the
first event.


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