issue: February 2009 APPLIANCE Magazine Electronics Report Flexible Control	Share  Printable format  Email this Article  Search
 An onboard LCD controller makes a new MCU series an affordable and flexible solution for design engineers.

The latest addition to the R8C family of microcontrollers (MCUs), the R8C/Lx series from Renesas Technology America Inc. (San Jose, CA, U.S.; www.renesas.com) offers engineers a built-in LCD controller and is capable of driving up to 416 LCD segments. According to the company, these features, along with other integrated features such as power-on-reset and on-chip oscillators, create a single-chip solution that reduces bill of material costs and design complexity.

“Electronics in a typical home appliance have to perform three main functions: system control, user interface, and safety/monitoring,� explains Nelson Quintana, product manager, system LSI business unit. “The R8C/Lx MCU integrates functional blocks to handle all three tasks.�

The MCU’s peripheral functions such as A/D, D/A, timers, and serial interfaces can be used in system control. Similarly, specialized hardware features such as detection of oscillator failure, an independent watchdog timer, and protection of system registers provide a self-testing mechanism to achieve a high level of safety and reliability. For the user interface, the MCU can control the most common input devices such as key matrices or knobs, and it can drive an LCD glass to enhance the operation of the appliance.

Quintana says that compared with other design options, an MCU with a built-in LCD controller provides more design flexibility. “Products incorporating an LCD can be typically designed using standard I/Os from any MCUs. This approach, however, has many limitations in the type and/or size of LCD glass that can be controlled, and the design can be complex since it is a software-based approach,� he explains.

A second approach is to use an LCD module that has a dedicated controller, also known as chip-on-glass. “Although this may be the easiest way to add an LCD to a product, it is definitely not the lowest-cost solution because of the addition of an extra chip,� Quintana says. “An MCU with a built-in LCD controller such as the R8C/Lx series provides greater flexibility, because the hardware can be configured for various options, thus reducing the software complexity and eliminating the cost of external components.�

Further adding to the device’s flexibility is the integrated data transfer controller (DTC). “The DTC unit can be configured to move data from any location in memory to any peripherals or vice versa,� Quintana explains. “In addition, the unit can be set to start transfers immediately after an interrupt trigger or with software control.�

In a motor control application for a washing machine, which requires the MCU to continuously monitor motor sensors through multiple A/D inputs, Quintana says the DTC can be configured to automatically transfer the A/D conversion results from the A/D registers to RAM for calculation purposes. “By doing so, the CPU will not be interrupted; hence, reducing the interrupt handling overhead,� he says.

Based on a 16-bit CPU core, the new device also integrates data flash memory with a background operation function that allows the CPU to execute instructions while data are being written to or erased from the data flash. It supports an extended voltage range of 1.8 to 5.5 V to give system designers options for configuring their power supplies, while potentially reducing system cost by eliminating unnecessary components. In addition, high-speed on-chip oscillators eliminate the need for an external resonator by proving precise clock signals at 40, 36.864, or 32 MHz.

In addition to an integrated data transfer controller, data flash, and an onboard 416-pixel LCD controller, the R8C/Lx MCU features hardware for self-testing to facilitate industry standards for safety.