National Semiconductor’s new mobile I/O companions unburden host processor to ease handheld device design

National Semiconductor Corporation offers designers an easy way to expand system functionality in portable products such as personal digital assistants, media players, instrumentation, medical equipment and mobile handsets.

Portable device manufacturers continue to differentiate their products through added features such as custom keyboards or special lighting. This increasingly requires a more flexible design approach to unburden the device’s main or host processor and reduce design time. National’s LM8322 and LM8333 mobile I/O companions allow designers to re-partition their systems by offloading tasks from the processor and adding features through a reconfigurable set of simple commands.

The flexible, modular single chips enable use of the same host processor and companion across multiple product versions. The LM8322 and LM8333 off-the-shelf integrated circuits include embedded key-scan functions, I/O expansion and light-emitting diode (LED) control capabilities.

Communication from the mobile I/O companion with the host processor is performed via a standard I2C compatible bus and interrupt signal that require only three pins, giving designers more options in placing the host processor on the board. A set of complex commands and scripts for pulse-width-modulation (PWM) signal generation allows the host to quickly configure the mobile I/O companion’s resources or trigger execution of commands.

Key Features and Benefits
Using the simple command set, the host processor can configure the LM8322 and LM8333 through an I2C compatible ACCESS.bus interface in slave mode up to 400 KHz. The fully tested and qualified companion chips dramatically reduce system design time and maintain accurate performance over the industrial temperature range of -40 degrees C to 85 degrees C.

The LM8322 supports keypad matrices up to 104 keys, while the LM8333 supports up to 72 keys. Both have eight special-function keys that take priority in the key rolling sequence. The on-chip clock, power-on-reset and on-chip oscillator require minimal external circuitry to support the mobile I/O companion’s operation.

By offloading the keyboard scanning feature to the companion, the host processor can enter sleep mode and reduce system power consumption. When there is no activity on the host bus or keypad, the companion automatically enters stand-by mode, typically consuming 18 uW.
The LM8322 has 1.62V-to-1.98V single-supply operation and up to 16 pins that can be configured as general-purpose I/O expansion for controlling additional peripherals. Its three independent, host-programmable PWM outputs can be used to generate more complex signals for adjusting an LED’s brightness or other sophisticated lighting effects.

Engineering Better Systems
Whether listening to high-fidelity audio, watching high-resolution video, or capturing and sharing multimedia files, National provides all the differentiating analog technology handheld devices need to minimize energy consumption and enhance users' experiences with longer battery life, better sound, sharper display images, smaller form factors, whiter lighting and streamlined interfaces. Working closely with customers and partners, National continues to define new architectures and standards, such as the PowerWise and Mobile Pixel Link technologies, that create unique features for portable devices. For detailed technical information about National’s other products for multimedia handheld devices, visit handheld.national.com.

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