LM8330 datasheet(13/54 Pages) TI2

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LM8330

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SNVS839A – JUNE 2012 – REVISED MARCH 2013

KEYSCAN PROCESS

The LM8330 keyscan functionality is based on a specific scanning procedure performed in a 4ms interval. On

each scan all assigned key matrix pins are evaluated for state changes.

In case a key event has been identified, the event is stored in the key event FIFO, accessible via the EVTCODE

KBDCODE[3:0] registers. As soon as the EVTCODE FIFO includes a event, the device sets the RAW keyboard

event interrupt REVTINT. The RSINT interrupt is set anytime the keyboard status has changed.

Depending on the interrupt masking for the keyboard events (KBDMSK) and the masked interrupt handling

(KBDMIS), the pin IRQN will follow the IRQST.KBDIRQ status, which is set as soon as one interrupt in KBDRIS

is set.

Figure 5 shows the basic flow of a scanning process and which registers are affected.

Figure 5. Example Keyscan Operation for

1 Key Press and Release

READING KEYSCAN STATUS BY THE HOST

In order to keep track of the keyscan status, the host either needs to regularly poll the IRQST register or needs

to react on the Interrupt signaled by the IRQN pin, in case the ball is configured for interrupt functionality. (See

GPIO FEATURE CONFIGURATION).

Figure 6 gives an example on which registers to read to get the keyboard events from the LM8330 and how they

influence the interrupt event registers. The example is based on the assumption that the LM8330 has indicated

the keyboard event by the IRQN pin.

Since the interrupt pin has various sources, the host first checks the IRQST register for the interrupt source. If

KBDIRQ is set, the host can check the KBDMIS register to define the exact interrupt source. KBDMIS contains

the masked status of KBDRIS and reflects the source for raising the interrupt pin. The interrupt mask is defined

by KBDMSK. The complete status of all pending keyboard interrupts is available in the raw interrupt register

KBDRIS.

After evaluating the interrupt source the host starts reading the EVTCODE or KBDCODE register. In this

example the host first reads the KBDCODE to get possible key press events and afterwards reads the complete

event list by reading the EVTCODE register until all events are captured (0x7F indicates end of buffer).

Reading KBDCODE clears the RSINT interrupt bit if all keyboards events are emptied. In the same way,

REVTINT is cleared in case the EVTCODE FIFO reaches its empty state on read.

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