AN3170| Application Note
Maxim/Dallas > App Notes > MICROCONTROLLERS Keywords: DS80C400, DS80C390, DS1672, DS2502, TINIm400, TINIs400, 8-bot microcontrollers
Apr 06, 2004
APPLICATION NOTE 3170
Finding the Middle Ground: Developing Applications with HighSpeed 8-Bit Microcontrollers
Software developers for personal computers have a number of advantages over embedded developers. Not only do they develop for systems that rival the power and memory of supercomputers of just a few years ago, but they develop for systems that generally already exist. Embedded developers, on the other hand, not only develop on much smaller systems, but they usually have to design the system first. An approach must be chosen based on the size of the problem. If the problem has little user interaction, controls a small number of devices, and is a relatively simple design, it can be tackled with a lowpower, 8-bit microcontroller, like an 8051, 68HC11, Amtel AVR, or PIC variant. These usually provide adequate power and flexibility. If the problem has large amounts of user interaction, needs to talk over Ethernet, or needs to talk to complex devices like digital cameras, then usually a PC-104, StrongARM, or another type of "one-calorie personal computers" is used. These generally provide abundant processing power,
complex operating systems, and large amounts of RAM. There is a gray zone in between. For example, let's say Joe's Security Service is entering the cutthroat market of network door locks. Due to recent security alerts, companies want to install door locks that log users with more than just an ID number. They want electronic door locks that take a photo of either the person's face or their thumbprint whenever the user wants to open the door. These images are sent over a network to a central server either for logging or, in a complex example, image recognition and validation. If the image is validated, the server sends back a response to the network door lock, and the door opens for the user. Joe would like to have his customers install many doors throughout their facilities, so it is important to keep costs low. One of Joe's competitors, Alex's Security Central, is developing a network camera door lock using an 8-bit RISC connected to an Ethernet controller. Joe dismisses this solution as underpowered. He kn
ows that there have been a number of projects involving connecting these Harvard-architecture chips to an Ethernet controller. However, many of these projects are in their infancy, none of them are commercially supported, and the TCP/IP stack is limited by the architecture itself. If talking over the network did not disqualify them, talking to a digital camera would. An adequate image would require 40kB to 60kB of memory, which has to compete with the code memory space as well. Even if he was using something with non-Harvard architecture, there is just too much work to be done and data to be processed with a traditional 8-bit microcontroller. Joe's arch nemesis, Troy of Troy's X-Treme Security, is also developing a solution. Joe hates Troy because Troy has no respect for the art and finesse of embedded system design. For romance's sake, we will also say that Troy is dating Joe's ex-girlfriend, Amiga, who left Joe because he spent too much time at the computer (also known as an "occupational hazard" among emb
edded system developers). Troy is developing a solution using a StrongARM running Pocket PC, which has speedy I/O and networking capabilities. Joe sees this solution as overkill. Beyond taking a photo, the processor will sit idle most of the time. The ideal solution does not need a lot of memory or power, so running embedded Linux or Pocket PC would add unnecessary bloat, and too much cost, for such a simple device. What Joe needs is a microcontroller powerful enough to handle the network and the camera, but less expensive and functional than a 32-bit solution. It would help Joe if it supported a higher level language than pure assembly in order to simplify development. How will Joe be able to beat Alex's power, Troy's price, and win back his true love? Enter TINI .
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