LM8323 datasheet(13/46 Pages) TI2

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LM8323

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SNLS273A – JULY 2010 – REVISED MARCH 2013

Figure 7. Halt Current vs. Temperature at 1.98V

Halt mode is entered when no key-press event, key-release event, change in the rotary encoder counter value or

ACCESS.bus activity is detected for a certain period of time (by default, 500 ms). The mechanism for entering

Halt mode is always enabled in hardware, but the host can program the period of inactivity which triggers entry

into Halt mode.

NOTE

When FW4 version devices enter the Halt mode there is approximately a 33% chance the

device may miss key events during the period of 3ms before entering Halt mode until 3ms

after entering Halt mode resulting in lost key events. This was corrected in FW6 devices

so that 100% of all key events are captured, even as the device is entering Halt mode.

ACCESS.bus ACTIVITY

When the LM8323 is in Halt mode, any activity on the ACCESS.bus interface will cause the LM8323 to exit from

Halt mode. However, the LM8323 will not be able to acknowledge the first bus cycle immediately following wake-

up from Halt mode. It will respond with a negative acknowledgement, and the host should then repeat the cycle.

The LM8323 will be prevented from entering Halt mode if it shares the bus with peripherals that are continuously

active. For lowest power consumption, the LM8323 should only share the bus with peripherals that require little

or no bus activity after system initialization.

KEYPAD INTERFACE

EVENT CODE ASSIGNMENT

After power-on reset and host initialization, the LM8323 starts scanning the keypad. It stays active for a default

time of about 500 ms after the last key is released, after which it enters Halt mode to minimize power

consumption (typically <9 µA standby current).

Table 4 lists the codes assigned to the matrix positions encoded by the hardware. Key-press events are

assigned the codes listed in Table 4, but with the MSB set. When a key is released, the MSB of the code is

clear.

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LM8323 Datasheet(PDF) 13 Page - Texas Instruments