TCA8418E_15 Datasheet, PDF (18/50 Pages) Texas Instruments – I2C Controlled Keypad Scan IC With Integrated ESD Protection

TCA8418E
SCPS222C – MAY 2010 – REVISED OCTOBER 2015
www.ti.com
Consider the example below, if the FIFO is full of the key presses and a new key press comes in. This new
overflow key press will be a key press of key 2 (0x82 is the hex representation of a key 2 press event)
FIFO REGISTER
A
B
C
D
E
F
H
I
J
K
Table 7. Key Event Overflow Handling
ORIGINAL VALUE
0x81
0xA0
0x01
0x20
0x97
0x17
0xAD
0xA9
0x29
0x2D
AFTER KEY 1 PRESS EVENT (0x82)
OVR_FLOW_M = 1
OVR_FLOW_M = 0
0xA0
0x81
0x01
0xA0
0x20
0x01
0x97
0x20
0x17
0x97
0xAD
0x17
0xA9
0xAD
0x29
0xA9
0x2D
0x29
0x82
0x2D
8.3.2 Keypad Lock/Unlock
This user can lock the keypad through the lock/unlock feature in this device. Once the keypad is locked by
setting BIT6 in KEY_LCK_EC, it can prevent the generation of key event interrupts and recorded key events. The
unlock keys can be programmed with any value of the keys in the keypad matrix or any general purpose input
(GPI) values that are part of the Key Event Table. When the keypad lock interrupt mask timer is non-zero, the
user will need to press two specific keys before an keylock interrupt is generated or keypad events are recorded.
A key event interrupt is generated the first time a user presses any key. This first interrupt can be used to turn on
an LCD and display the unlock message. The processor will then read the lock status register to see if the
keypad is unlocked. The next interrupt (keylock interrupt) will not be generated unless both unlock keys
sequences are correct. If correct Unlock keys are not pressed before the mask timer expires, the state machine
will start over again.
The recommended procedure to lock the keypad is to do the following
1. Determine which keys will be used for the unlock sequence. The key value from the Key Event Tables needs
to be entered into the UNLOCK1 and UNLOCK2 registers.
2. The UNLOCK1 to UNLOCK2 timer duration must be set by entering the desired seconds (valid range is 0 to
7 seconds) into bits [2:0] of the KP_LCK_TMR register.
3. If an interrupt mask is desired (see Keypad Lock Interrupt Mask Timer), then the desired interrupt mask
duration (valid range is 0 to 31 seconds) must be entered into bits [7:3] of the KP_LCK_TMR register.
4. When the host is ready to lock the keypad, a 1 is to be written to the K_LCK_EN bit (BIT6) in the
KEY_LCK_EC register. This will lock the keypad.
5. If the host wishes to manually unlock the keypad, writing a '0' to the K_LCK_EN bit (BIT6) in the
KEY_LCK_EC register will unlock the keypad.
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