MCU Family Cuts Power, Expands LCD Drive Capability

I had a conversation with David Niewolny, a Freescale product marketing manager, about the company’s new “LL64″ processor, a member of the MC9S08 family, and thus properly called the MC9S08LL64. David explained Freescale developed this microcontroller (MCU) primarily for portable and industrial devices that can benefit from low power consumption and the capability to drive as many as 288 LCD segments. Rather than cover the MCU’s detailed specs, you can find them in the November 19, 2009 press release at: media.freescale.com/phoenix.zhtml?c=196520&p=irol-newsArticle&ID=1356929.

From my perspective, the chip’s low-power consumption, large Flash memory capacity, time-of-day clock, and wide array of development tools–along with the expanded LCD segment drive capability–make the MCU attractive. Freescale specifies a power consumption below 350 nA when the processor remains in its stop mode. That low current amount makes the ‘LL64 device attractive to developers who build battery-operated equipment that runs intermittently.

When designers create a product that will operate from two AA batteries, for example, they must consider when during the battery-discharge cycle their product will cease to operate. Many circuits will cut out before the batteries drop to 0.9V each, or 1.8V for each battery. Flash memories, for example, usually need more than 1.8V to update information, so the battery capacity between the Flash-memory write-voltage cutoff and the end-of-life voltage for two cells–1.8V–represents energy that goes in the trash. Or, more frequent battery-recharge cycles. The Flash memory in the ‘LL64 MCU, though, will continue to operate down to 1.8V, a nice power-saving advantage for designers.

On the LCD side, the ‘LL64 offers designers eight “backplanes” and 36 drive lines for a total of 288 individually-addressed segments or symbols on an LCD. The MCU will directly drive an LCD module, often called “the glass” in industry jargon. Designs do not need a separate LCD-driver IC. If a product does not require all 288 segments, the MCU can assign the unused pins to general-purpose I/O (GPIO) ports.

The MCU will flash one segment, even when stopped. There’s no need to wake up the processor periodically, change the segment’s state, go back to sleep, and repeat the process. The flashing segment could indicate “still working” or some other state to a product’s user.

To help designers get off to a quick start with a design for or evaluation of an ‘LL64 MCU, Freescale offers its “Tower System” (TWR-S08LL64-KIT) package for $US 99. If you have a Tower System, you can purchase just the MCU card (TWR-S08LL64), which comes with an LCD, pushbuttons, and other I/O devices, for $US 69. I have a Tower System, so I can just swap the MCU board. (See photo.)

Freescale also provides a complementary (free) edition of the CodeWarrior Development Studio for Microcontrollers (ver 6.3) software-development tools and its Processor Expert add-in. The latter tool produces a graphical screen that lets developers choose the MCU functions they need and then uses an automatic code generator to create known-good C code to control the MCU resources. But instead of churning out chip-specific code, the Processor Expert creates a hardware-abstraction layer that moves developers another step away from bit-bashing hardware control, but instead uses an application programming interface (API) that simplifies moving code between Freescale’s MCU families.

Find online training, webcasts, technical documents, and application notes at: www.freescale.com/lcd, and at: www.freescale.com/tower.

The Tower Geeks Web site also provides an independent source of information as well as forums about the Tower System: www.towergeeks.org. I’m a member. –Jon Titus