Using the MAX7359 for multifunctional and gaming keys on PDAs/smart phones

The keypad control properties of cellphone chipsets are often stretched to their limits when an OS or application needs to detect multiple keypresses (e.g. Ctrl-Alt-Del and gaming controls).

The MAX7359 is a low-power-consumption, special-purpose key-switch controller suitable for cellphones, printers, and other portable applications. Up to 64 keys can be implemented with this device. Separate keypress and release codes are assigned for every key. Multiple keys can be pressed simultaneously and/or held and released in different orders. Up to 16 keypress and release entries can be held in a FIFO register. Key-activity information collected by the MAX7359 is read through a simple I?C interface at one keypress or release entry per byte. To enhance the device's noise immunity, the detection of a keypress can be debounced. In other words, each pressed key is scanned twice within a very short time interval before it is detected.

To reduce power consumption, the MAX7359 consumes only 1.2?A in sleep mode while waiting for key activities. Upon a keypress, the controller wakes up in less than 200?s to collect the keypress/release information. After a specified key-activity idle time of between 0.256s and 8s, the device re-enters sleep mode. Note that key FIFO information can be accessed even in sleep mode. To relieve the host from permanent attention, an interrupt signal can be generated once a key is pressed or when the FIFO has reached a predefined amount of entries. The interrupt signal can be cleared by reading the device through the I?C interface or when the FIFO is emptied.

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