May 2005
Beginner to intermediate
398 pages
12h 12m
English
Content preview from Designing Embedded Hardware, 2nd Edition
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Electrical Characteristics
Pick up any chip datasheet and you will find three sections, labeled Absolute Maximum Ratings, DC Electrical Characteristics, and AC Electrical Characteristics. These are vitally important, but often poorly understood. So let's see what it all means, and how you work with that information to produce a reliable and effective embedded system. Let's look at the Absolute Maximum Ratings first.
Absolute Maximum Ratings
The very first thing you'll see in the electrical characteristics section is something labeled Absolute Maximum Ratings . A chip will be designed to operate under certain nominal conditions, and exceeding those conditions during normal operation is not advised. But what happens if you do go beyond those parameters? At just what point will you really kill the chip? The Absolute Maximum Ratings tell you just that. They show you how far you can stress the chip, and (sometimes) for how long, before the device will fail.
An example of the Absolute Maximum Ratings for a chip, in this case a Dallas Semiconductor DS87C550 microcontroller, is shown in Table 4-1.
Table 4-1. Absolute Maximum Ratings for a DS87C550 microcontroller
|
Parameter |
Rating |
|---|---|
|
Voltage on any pin relative to ground |
-0.3 V to (VCC + 0.5V) |
|
Voltage on VCC relative to ground |
-0.3 V to 6.0 V |
|
Operating temperature |
-40°C to +85°C |
|
Storage temperature |
-55°C to +125°C |
|
Soldering temperature |
160°C for 10 seconds |
So what does it all mean? Let's work through it. The first row of the table refers ...
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