.KEYWORD dragonball
.FLYINGHEAD DEEP INSIDE YOUR PALM DEVICE
.TITLE How Palm was able to make the Palm V so small
.FEATURE
.SPOTLIGHT FIGALT dragonball-cover.gif
.SUMMARY PalmPower scores another exclusive this month with this important article by Motorola engineer Brian Smith. If you’ve been wondering how Palm managed to make the Palm V so small, now you can find out. Although by nature technical, this article makes understanding the functions of the processor inside the new Palm V and Palm IIIx devices clear to everyone.
.AUTHOR Brian Smith
Powering the original Pilot devices, the PalmPilot Personal and Professional organizers, and the Palm III product families has been the DragonBall MC68328 Integrated Microprocessor from Motorola. The next generation of processor, the DragonBall EZ MC68EZ238 Integrated Microprocessor is at the heart of the recently introduced Palm IIIx and Palm V devices.
.CALLOUT The processor core provides 2.7 MIPS of performance, roughly twice the computing power of the original Macintosh computer.
In addition to Palm connected organizers, DragonBall family members can be found in a wide variety of consumer products from many vendors, such as pagers, fishfinders, educational products, toys, and communications devices. In addition, DragonBall family members power many other applications demanding integrated system-on-a-chip solutions that can function in cost-sensitive and battery-powered applications. Motorola’s PageWriter 2000 2-Way ReFLEX Pager also uses a DragonBall processor.
.H1 Background
A microprocessor is essentially a computational engine that is built to perform a set of operations. When combined with a program, or a list of instructions (such as the Palm OS), and a method for information input and output (such as a touch-screen or keyboard), a microprocessor can become a very useful tool. In a PC, the processor is accompanied by many other separate components that perform such functions as display control, memory control, user input, data storage and power management.
Motorola’s DragonBall family integrates the essential functions necessary to build handheld and embedded computer systems into a single piece of silicon. DragonBall EZ brings together the processor core, display controller, memory controller, sound generation, communication, and power management in a single component.
The DragonBall family was created at Motorola Semiconductor’s design facility at the Tai Po Industrial Estate in Hong Kong. From its initial vision, it has been built for the needs of small, cost-sensitive and battery-powered applications.
The DragonBall EZ microprocessor provides the functionality of many devices that used to exist as separate components on a single piece of silicon.
.H1 Processor core
At the heart of the DragonBall EZ is the 68EC000 microprocessor core. This is a version of the original 68000 microprocessor from Motorola, optimized for low power consumption and high performance. It runs at a clock speed of 16MHz (or 16 million cycles per second). The EC000 core provides 2.7 MIPS of performance, roughly twice the computing power of the original Macintosh computer.
.H1 Memory subsystem
Perhaps the most important part of a computing system is the memory subsystem, where the instructions and data of the processor are stored. The original DragonBall included a System Integration Module (SIM) that allowed it to interface to a variety of memory types, including SRAM, EPROM and FLASH. While this provided a good solution for most applications, battery powered systems (such as the Palm devices) required memory that maintained its contents with minimal power consumption when the unit was in standby mode. Coincidentally, a Palm device spends most of its life in a low power standby mode, even when it’s on.
FLASH memory maintains its contents without power, but is rather slow in retrieving and storing data. Since one of the important requirements of the Palm device is immediate responsiveness, engineers at 3Com had to use a type of SRAM called pseudo-static RAM or PSRAM. PSRAM is fast like conventional SRAM, but also has the ability to maintain its data with much lower power consumption than SRAM, thus enabling quick access and storage in a system that can run on a battery.
DragonBall EZ improves on the SIM of the original 68328 (used in ealier Palm devices) by adding a memory controller capable of supporting DRAM. The PC industry has made DRAM a very cheap commodity, as well as driving it to lower power consumption and higher density for portable computers.
DragonBall EZ supports both fast page (FP) and extended data out (EDO) types of DRAM, and has circuitry that supports self-refresh DRAM. This type of DRAM is specialized for low power applications by allowing the DRAM to refresh itself, or restore the values in its cells to prevent data loss. The DRAM controller in DragonBall EZ is tightly coupled with the power management circuitry on the chip to allow the DragonBall EZ processor to supervise the maintenance of the data in the DRAM chips.
The Palm IIIx and Palm V devices utilize the DRAM controller on DragonBall EZ along with the prevalence of low cost, low power DRAM components to provide larger memory spaces with fewer components and lower power consumption.
.H1 Enhanced LCD controller
The original DragonBall included a powerful display controller that could display information on a single monochrome or STN (supertwist nematic) LCD panel. It provided a glueless (i.e., direct connection) interface to a wide variety of panels available from manufacturers in the marketplace, such as Motorola, Sharp, Hitachi, Toshiba, Epson and many others. The display controller supported up to 4 grey levels (or shades of grey), and it provided an interface where a portion of the main system memory could be used as the display memory. This helped reduce design complexity and system cost by not requiring a separate display buffer, as found in many desktop computers.
DragonBall EZ improves on the LCD controller of the standard DragonBall by allowing supporting up to 640×512 pixels (although current Palm devices are limited to 160×160 pixels), with support for 16 gray levels. This helps increase the quality of the image presented to the user by allowing finer control of the darkness of each pixel. In addition, DragonBall EZ provides a pulse width modulator (PWM) that allows for electronic control of the contrast function on many LCD screens. The Palm V product utilizes this PWM to provide contrast control via an electronic adjustment rather than the manual knob found on previous Palm connected organizers.
.H1 Enhanced PWM controller
The pulse width modulator (PWM) in DragonBall EZ has been enhanced to be more programmable by the software developer. A PWM is often used to generate tones or sounds by generating a waveform that is input into a low pass filter and a speaker. The EZ PWM provides eight bits of resolution as well as a five byte FIFO (i.e., first in, first out) to increase performance and quality of tones generated. Both the Palm IIIx and Palm V organizers utilize this new PWM to increase the quality of the tones generated by the Palm device.
.H1 Smaller package, improved features
One of the main objectives of the DragonBall EZ was to reduce the physical size of the processor chip while also reducing cost. In this effort, a number of tradeoffs were made to reduce the number of pins on the package. The number of pins correlates directly to the cost of the package as well as the size of the package.
DragonBall EZ reduces the number of Serial Peripheral Interconnect (SPI) ports from two to one. An SPI port is used to talk to another component of the system, such as a keyboard, touchscreen controller, or a communications subsystem such as a modem or wireless data modem. Wireless data modems can transmit data over cellular networks, packet data networks, or even FLEX paging networks. An SPI connection consists of a master (the controller of the data interface) and the slave (the subservient device in the system). Most applications did not have the need for two separate ports simultaneously (one master and one slave) as offered on the Standard DragonBall, so the decision was made to eliminate one of the two SPI ports, leaving a master port only in DragonBall EZ.
DragonBall EZ implements a single UART (Universal Asynchronous Receiver/Transmitter) that is capable of IrDA 1.0 speeds of up to 115Kbps. IrDA is the protocol spoken by the infrared transceiver found in the Palm III connected organizer, and allows the exchange of data between Palm devices using light not visible to the human eye. Infrared technology has been around for some time in remote controls for consumer devices, but the IrDA standard allows the exchange of data at rates up to 100 times as fast. In addition, the UART is also traditionally used to provide communications between systems, such as the HotSync functionality and modems found on Palm organizers. The integration found in DragonBall EZ allows IrDA implementations with minimal external components, translating into greater cost savings for system designers.
In addition, DragonBall EZ reduces the number of timers from two channels (as in standard DragonBall) to one channel. A timer is used to measure the length of time between events defined by the programmer. When the time limit is reached, an interrupt is generated to tell the processor core to stop what it is doing and perform the task that the programmer defined to happen when the timer expired. Reducing the number of timer channels from two to one decreases the pin count of DragonBall EZ while still maintaining the facilities necessary for most systems.
While eliminating some of the non-essential features, DragonBall EZ retains many features found in the standard DragonBall. These features include a real time clock (RTC), allowing the processor to keep time as well as an interrupt controller that helps programmers handle asynchronous events, such as when you tap on the screen to select an item or to write a character in Graffiti.
The combination of these tradeoffs along with sharing pins with many signals and functions (called multiplexing), allowed the pin count to be reduced from 144 in the original DragonBall to 100 in the DragonBall EZ. DragonBall EZ is available in two packages: a 100-pin TQFP (Thin Quad Flat Pack) and a 144-pin BGA (Ball Grid Array). Both of these packages have about 50% of the footprint of the original DragonBall, and the BGA is incredibly thin, allowing systems to be built in thinner enclosures. A smaller package allowed the Palm IIIx and Palm V developers to reduce the size of their printed circuit board, and the BGA package helps the Palm V device achieve its thin form factor.
.H1 Better system debug capability
DragonBall EZ enhances the facilities built into the device to ease system development. It adds circuitry that allows the UART to be reconfigured to initialize the processor and download program instructions and data into memory. It then can be used to control the processor while running this code. DragonBall EZ also adds built-in emulation functions such as a dedicated memory space for the emulator debug monitor, a dedicated interrupt for emulation, and hardware support for breakpoint instruction insertion. All of these features assist the system designer and programmer, allowing them to control the system and quickly examine the results of their work.
.H1 Power consumption
The "system on a chip" inside the DragonBall EZ allows system designers to minimize external components necessary for a system, thereby reducing overall system power. The DragonBall EZ runs at 3.3V and consumes only 20mA in typical operation. The power management circuitry in DragonBall EZ allows each unit in the chip (LCD controller, memory controller, UART, SPI, etc.) to be shut off when not in use, thereby increasing the power savings. The DragonBall EZ is a "fully static" design, which means that when portions of the chip are not being used, their transistors (the elemental building blocks of a microprocessor) are not switching on and off, and thus not burning any power. The combination of power management along with miserly transistors allows DragonBall EZ powered devices to run weeks on standard batteries.
.PAGE
.H1 Looking into the future
DragonBall EZ provides a new level of integration for embedded computing platforms while reducing cost, package size and power consumption. Motorola will continue to work to improve integration, performance, power consumption and cost. In addition, Motorola Semiconductor will bring advanced silicon solutions and advanced wireless technology to DragonBall-based systems, empowering the next generation of Palm Computing Platform and other embedded devices well into the next millennium.
.BEGIN_SIDEBAR
.H1 Product availability and resources
For more information on the DragonBall EZ and DragonBall family of processors, please consult the Motorola DragonBall website at http://www.mot.com/dragonball.
An earlier PalmPower article about the original DragonBall processor is at http://www.palmpower.com/issues/issue199805/processor001.html.
.END_SIDEBAR
.BIO Brian Smith is a Market Development Applications Engineer for Motorola SPS. He can be reached via email at dragonballez@hotmail.com.
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