Post by thread:FPGA's, FPLD's, etc.

|In my original question, I referred to using the LED modules with cascaded |595s, but that was just an example. I ask the question .. well .. because |I didn't know the answer <g>. I have read every response and was actually |able to follow some of them :). I have often seen references to FPGAs and |PGAs and wondered about their use. How are these devices used ? Do you use |some type of programmer to program them to perform a specific function ? Generally, field programmable logic devices and gate arrays are devices which can be "programmed" to act like a variety of digital electronic circuits. Some of these devices are fairly simple; some are much more complex. Generally, they fall into three types: At the bottom end are PAL's and GAL's [GAL stands for "general array logic"]; the primary distinction between these two types is that GAL's are generally reprogrammable while PAL's are generally one-time-prog- rammable. Note that unlike most OTPROM, many PAL devices are physic- ally altered by programming and so could not be erased by UV exposure even if the package were windowed. The 22V10 is a typical GAL device, produced by many vendors. On the 24-pin DIP version, pins 1-11 and 13 are input-only, pin 12 is ground, pins 14-21 are configurable input/output, and pin 24 is VDD. Each output may optionally include an edge-triggered latch (clocked by pin 1) and includes a 3-state buffer (which may be set to "always on" or "always off" if desired). The 12 inputs and 10 I/O's are fed into the main logic array; the array has about 100 rows, each of which will look for the 22 inputs to be "high", "low", or "don't care" and will output high iff all of the required inputs are correct. Ten of these outputs drive the 3- state buffers on the I/O pins, a few have special functions, and most of them are fed into 10 many-input "OR" gates (one for each I/O pin). The output of each "or" gate may optionally latched and/or inverted, and is then fed to the output pin. Using the above facilities, many types of logic may be implemented; a 4-bit counter could be implemented on pins 18-21 by enabling the latches on those pins, and then setting... pin18 high iff pin18 was low. pin19 high iff (pin18 was high and pin19 was low) or (pin19 was high and pin18 was low) pin20 high iff (pin18 was high and pin19 was high and pin20 was low) or (pin20 was high and pin18 was low) or (pin20 was high and pin19 was low) pin21 high iff (pin18 was high and pin19 was high and pin20 was high and pin21 was low) or (pin21 was high and pin18 was low) or (pin21 was high and pin19 was low) or (pin21 was high and pin20 was low) Note that the 22V10 allows any number of items in each "and" term, but only has about 10 "and" terms which can be "or"'ed together for each pin. Although this is often not a problem, some types of logic can require a lot of terms; the upper stages of a normal binary counter will require one term per bit, and a gray-code counter could need many dozens of terms. For these applications, some higher-end PLD's or PGA's may be more suitable... ... more tomorrow.

owa owa owa, hold your horses... this is not true. There are some pl devices that can drain 420mA at 4MHz. :) It is almost 2.5Watts!!! A heatter!!!, at least no humidity. Philips PHD48N22-7 is 420mA, Philips 10H20EV8 is 250mA. So, as you can see, much more than you said. :) Wagner. William Chops Westfield wrote: {Quote hidden}> > When talking about PIC circuitry, one must remember that "typical" GALs > and such are real power-pigs, with the "quarter power" devices still > consuming more in an idle state than a PIC running at full speed. There > are apparently lower power GALs, but they're much less common... > > (full power GAL like 22V10 = ~100mA...) > > In fact, one of the first possible applications of PICs that I thought of > was as a lower-power (and more general) replacement for GALs and such > (when speed was not a requirement.) > > BillW