8.5 COMMAND EXECUTION SUMMARY

•

With the interrupt, status, and error codes, the LM8333

provides the features needed to support a reliable key-

scan functionality.

•

Up to 14 key-scan events can be stored in an internal

FIFO buffer. The end of buffer is indicated with the 00

(empty character) code.

•

The host can repeatedly read the FIFO without modifying

the FIFO pointer using the RPT_FIFO_READ command

(0x21), for example if an error is encountered during a

read.

•

The LM8333 asserts the IRQ output low when a new

character is pressed after the last interrupt acknowledge

from the host. The IRQ output will be deasserted after the

host has acknowledged the interrupt by reading the inter-

rupt code using the READ_INT command (0xD0).

•

The host can synchronize with the LM8333 by reading

the status code with the READ_STAT command (0xE0).

The status code verifies whether the last command was

successfully completed.

•

Two GPIO pins on the LM8333 may be configured as

external interrupt inputs. A rising or falling edge on an

enabled interrupt input triggers wake-up from Halt mode

and asserts an interrupt to the host by pulling the IRQ

output low.

•

The host can change the debounce time from the default

time of 10 ms. This can be used for reliable scanning of

keyboards with noisy contacts. The debounce time can

be set to about 1 second in steps of 4 milliseconds. The

debounce time is set with the DEBOUNCE command

(0x22).

•

The host can change the active time permitted before

entering Halt mode from the default period of 500 ms.

The active time is the time during which the keypad is

scanned after the last key is released, before entering

Halt mode. The active time must be longer than the

debounce time.

•

The host can program the direction and output state of

four general-purpose I/O pins. The host can also read the

states on these pins.

•

The host can program a 16-bit timer for generating a

PWM output. If the PWM function is not used, the PWM

pin can be used as a general-purpose output.

20210613

FIGURE 11. Interrupt Processing

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