LM8322JGR8/NOPB National Semiconductor, LM8322JGR8/NOPB Datasheet - Page 15

• Manufacturer Part Number: LM8322JGR8/NOPB
• Description: IC MOBILE I/O COMPAN 36MICRARRAY
• Manufacturer: National Semiconductor

Specifications of LM8322JGR8/NOPB

• Applications: *
• Mounting Type: Surface Mount
• Package / Case: 36-Micro Array
• For Use With: LM8322EVALKIT - BOARD EVALUATION LM8322
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: LM8322JGR8; LM8322JGR8TR

During a scan cycle, only one KP-Yx output pin will be driven
low at any time, while the others are driven high or undriven.
At the time scale used in Figure 8, the low phase of a KP-Yx
output during a scan cycle is not visible. The KP-Xx input pins
are pulled high by weak pullups.
There are capacitive loads on the KP-Xx inputs and KP-Yx
outputs due to protection circuits, wiring, etc. The LM8322 in-
serts delays to allow complete charging or discharging of
these loads before sampling the input levels on the KP-Xx
inputs. The maximum parasitic load capacitance on the KP-
Xx inputs is 5 nF.
After detecting a key-press or key-release event, the de-
bounce time specified by the SET_DEBOUNCE command
(0x8F) sets the minimum time for confirming the event before
the IRQ output is asserted.
If more than two keys are pressed simultaneously, the pattern
of key closures may be ambiguous, in which case the the in-
terrupt code indicates an error and the IRQ output is asserted
(if enabled).
The SF keys connect KP-Xx inputs directly to ground. There
can be up to eight SF-keys. If any of these keys are pressed,
other keys that use the same KP-Xx pin are ignored.
12.2.1 Timing Parameters
Two timing parameters affect scanning of the keypad:
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12.2.2 Multiple Key Pressings
If more than two keys are pressed at the same time, the
LM8322 stores all key pressed and released events in the
FIFO buffer in the sequence in which they were decoded.
For multiple key pressings the following circumstances have
to be respected:
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•
Debounce Time — minimum delay between detecting a
keypad event and confirming the event before asserting
IRQ. The default debounce time is 3 scan cycles (about
12 milliseconds), but the host can set values in the range
1–255 cycles (4–1020 milliseconds).
Active Time — period without detecting a state change in
the keypad that triggers entry into Halt mode, during which
keypad scanning is suspended. The default active time is
500 milliseconds, but the host can set it values in the range
4–1020 milliseconds. The active time must be greater than
the debounce time.
A multiple key-press event is given if two or more key-
press events are reported but no corresponding key-
release event.
With the activity time set between the minimum and
maximum time (4 msec to 1 second) it is not safe to detect
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“As soon as the host device has detected a key pressed event
the host must send the SET_ACTIVE Command with the pa-
rameter set to “00”. This will prevent the LM8322 from enter-
ing HALT mode. If all keyboard events are resolved (no
remaining key pressed status in the LM8322 anymore) then
the host must send the SET_ACTIVE Command again with
the parameter setting the desired duration for the active time.
This will enable the LM8322 to enter low power HALT mode
once the activity time has passed without detecting any
events.
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12.3 EXAMPLE KEYPAD CONFIGURATION
Figure 10 shows an 8 × 4 keypad matrix. This configuration
occupies all scanning inputs (KP-X0 through KP-X7) and four
scanning outputs (KP-Y0 through KP-Y3). The remaining
scanning outputs KP-Y4 through KP-Y11 are available for use
as GPIO pins.
two simultaneous key pressings in one input row (see
Figure 9 on the left hand side.)
If all key pressings (two or more) are located in different
input rows (see Figure 9 on the right hand side) then the
key pressed events will be correctly found in the FIFO
buffer without any restriction.
In order to securely detect and store the key codes of
simultaneous key pressings in the same input row the
following precautions must be taken from the host side:
Once one or more key (pressed and/or released) events
have been read from the host with the help of the READ
FIFO command there are two conditions cleaning the
FIFO buffer contents:
— A second execution of the READ FIFO Command or,
— A new key event detected from the LM8322.
FIGURE 9. Simultaneous Keys Pressed
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