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WHATýS THE LOGIC BEHIND THE DESIGN?

Working with Programmable Logic

by George Martin

Start ý The Search Begins ý Navigating ý Counting the Ways ý Simulation ý Sources and PDF

I was watching CSPAN one evening and Scott McNealy of Sun Microsystems was on talking about Microsoftýs new .NET initiative. Thatýs an interesting topic by itself, but the part I found exciting was his list on new products. Remember last monthýs article?

The new product that caught my attention was a unit that monitors the tire pressure in your car. Scott, of course, has it Java/web-enabled so that it reminds you when tire pressure is low and then sends an e-mail to the manufacturer. He suggested that a rollover sensor could work the same way and call for help whenever the car was upside down. If you think about it, all the necessary components are already available for such a system. It just needs to be implemented. Thereýs another good product idea for you.

If youýve ever had to program logic devices, youýve probably used a text-based programming language such as PALASM or ABEL. I was first introduced to programmable logic with the Advanced Micro (AMD) MACH devices. In the lateý 80s, AMD had a traveling presentation that was given by the actual designers of the compiler. That presentation added to my knowledge base and has kept me up to date since.

Those early PLD devices started as 20-pin ICs. Using one pin for power and one for ground, that left 18 pins for inputs and outputs. The simple 16L8 device had 10 inputs, six input/outputs, and two output pins. The latched version (16R8) had one clock pin, one output enable pin, eight input pins, and eight output pins. I did a lot with these devices, filling them to 98% of capacity. These devices had more pins and more logic, as well as custom organizations for specific applications such as state machines.

The next big step along the integration curve was to place four copies of the eight-register devices in a single package. Soon after, devices similar to AMDýs MACH 110 started appearing. The MACH 110 was a 44-pin PLCC package with two clock inputs, five general-purpose inputs, and four banks of eight registers each for input/output. Also offered was the MACH 210, which had an additional four banks of eight registers. These additional registers could be used as buried logic devices and did not appear at the pins. These were great for long counters that had no need to report intermediate results or status. However, it became difficult to write all the code and run simulations on a complicated designýtoo many pages and too difficult to follow.

Well, itýs over 20 years later and times are changing. AMD spun the PLD business into a separate company named Vantis. Vantis was then purchased by Lattice Semiconductor.

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