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ADP5589CP-EVALZ Datasheet(PDF) 9 Page - Analog Devices

Part No. ADP5589CP-EVALZ
Description  Keypad Decoder and I/O Expansion
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Maker  AD [Analog Devices]
Homepage  http://www.analog.com
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ADP5589CP-EVALZ Datasheet(HTML) 9 Page - Analog Devices

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Data Sheet
ADP5589
Rev. B | Page 9 of 52
DETAILED DESCRIPTION
EVENT FIFO
It is important to understand the function of the event FIFO.
The ADP5589 features an event FIFO that can record as many
as 16 events. By default, the FIFO primarily records key events,
such as key press and key release. However, it is possible to
configure the general-purpose input (GPI) and logic activity
to generate event information on the FIFO as well. An event
count, EC[4:0], is composed of five bits and works in tandem
with the FIFO so that the user knows how much of the FIFO
must be read back at any given time.
The FIFO is composed of 16 eight-bit sections that the user
accesses by reading the FIFO_x registers. The actual FIFO
is not in user accessible registers until a read occurs. The
FIFO can be thought of as a “first in, first out” buffer used
to fill Register 0x03 to Register 0x12.
The event FIFO is made up of 16 eight-bit registers. In each
register, Bits[6:0] hold the event identifier, and Bit 7 holds the
event state. With seven bits, 127 different events can be identified.
See Table 11 for event decoding.
EVENT1[7:0]
EVENT8_IDENTIFIER[6:0]
EVENT2[7:0]
EVENT3[7:0]
EVENT4[7:0]
EVENT13[7:0]
EVENT14[7:0]
EVENT15[7:0]
EVENT16[7:0]
EVENT5[7:0]
EVENT6[7:0]
EVENT7[7:0]
EVENT8[7:0]
EVENT9[7:0]
EVENT10[7:0]
EVENT11[7:0]
EVENT12[7:0]
7
EVENT8_STATE
FIFO
UPDATE
GPI EVENTS
EC[4:0]
OVRFLOW_INT
KEY EVENTS
LOGIC EVENTS
6
5
4
3
2
1
0
Figure 7. Breakdown of Eventx[7:0] Bits
When events are available on the FIFO, the user should first
read back the event count, EC[4:0], to determine how many
events must be read back. Events can be read from the top of
the FIFO only. When an event is read back, all remaining events
in the FIFO are shifted up one location, and the EC[4:0] count
is decremented.
KEY 3 PRESSED
KEY 3 RELEASED
GPI 7 ACTIVE
EC = 3
FIRST
READ
KEY 3 RELEASED
GPI 7 ACTIVE
EC = 2
SECOND
READ
GPI 7 ACTIVE
EC = 1
THIRD
READ
EC = 0
Figure 8. FIFO Operation
The FIFO registers (0x03 to 0x12) always point to the top of the
FIFO (that is, the location of EVENT1[7:0]). If the user tries to
read back from any location in a FIFO, data is always obtained
from the top of that FIFO. This ensures that events can only be
read back in the order in which they occurred, thus ensuring
the integrity of the FIFO system.
Some of the onboard functions of ADP5589 can be program-
med to generate events on the FIFO. A FIFO update control
block manages updates to the FIFO. If an I2C transaction is
accessing any of the FIFO address locations, updates are paused
until the I2C transaction has completed.
A FIFO overflow event occurs when more than 16 events are
generated prior to an external processor reading a FIFO and
clearing it.
If an overflow condition occurs, the overflow status bit is set.
An interrupt is generated if overflow interrupt is enabled,
signaling to the processor that more than 16 events have
occurred.
KEY SCAN CONTROL
General
The 19 input/output pins can be configured to decode a keypad
matrix up to a maximum size of 88 switches (11 × 8 matrix).
Smaller matrices can also be configured, freeing up the unused
row and column pins for other I/O functions.
The R0 through R7 I/O pins comprise the rows of the keypad
matrix. The C0 through C10 I/O pins comprise the columns of
the keypad matrix. Pins used as rows are pulled up via the internal
300 kΩ (or 100 kΩ) resistors. Pins used as columns are driven
low via the internal NMOS current sink.


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