TCA8418E_15 Datasheet, PDF (17/50 Pages) Texas Instruments – I2C Controlled Keypad Scan IC With Integrated ESD Protection

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TCA8418E
SCPS222C – MAY 2010 – REVISED OCTOBER 2015
5. Reset the INT_STAT interrupt flag which was causing the interrupt by writing a 1 to the specific bit.
As an example, consider the following key presses.
EVENT NUMBER
1
2
3
4
5
6
7
8
9
10
Table 4. Example Key Sequence
KEY (DECIMAL VALUE)
1
32
1
32
23
23
45
41
41
45
PRESS/RELEASE
Press
Press
Release
Release
Press
Release
Press
Press
Release
Release
If this example key sequence occurs, then while performing the recommended read procedure listed above, the
host would see the following information. Information at the top of the list is of an initial read to the
KEY_LCK_EC[3:0] register.
KEY_LCK_EC[3:0] VALUE
10
9
8
7
6
5
4
3
2
1
0
Table 5. Example Key Sequence
KEY_EVENT_A VALUE
(BINARY/HEX)
N/A
1 000 0001 (0x81)
1 010 0000 (0xA0)
0 000 0001 (0x01)
0 010 0000 (0x20)
1 001 0111 (0x97)
0 001 0111 (0x17)
1 010 1101 (0xAD)
1 010 1001 (0xA9)
0 010 1001 (0x29)
0 010 1101 (0x2D)
KEY (DECIMAL VALUE)
N/A
1
32
1
32
23
23
45
41
41
45
PRESS/RELEASE
N/A
Press
Press
Release
Release
Press
Release
Press
Press
Release
Release
8.3.1.4 Key Event Overflow
The TCA8418E has the ability to handle an overflow of the key event FIFO. An overflow event occurs when the
FIFO is full of events (10 key events are stored) and a new key event occurs. In short, this means that the
TCA8418E does not have the ability to hold any more key press information in the internal buffer. When this
occurs, the OVR_FLOW_INT bit in the INT_STAT Register is set, and if the OVR_FLOW_IEN bit is set in the
CFG Register, then the INT output will be asserted low to let the processor know that an overflow has occurred.
The TCA8418E has the ability to handle an overflow in 1 of two ways, which is determined by the bit value of the
OVR_FLOW_M bit in the CFG Register.
OVR_FLOW_M VALUE
1
0
Table 6. OVR_FLOW_M Bit
OVERFLOW MODE
Enabled
Disabled (Default)
BEHAVIOR
Overflow data shifts with last event pushing first event out
Overflow data is not stored and lost
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