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.

Figure 20. Keypad Lock Flowchart