Hi All,

I planned to introduce myself into the world of GALs for more simple glue logic instead of "heavy" network of 74HC ICs. But as far as I can see I am out of sync of the world: is my view correct that GALs are treated as deprecated in general? All the vendors datasheet I wanted to check told me that these devices are no longer produced/supported/etc. I am not sure what can I do now, is it a good idea to build on a top of devices which are about dying? Others told me, that I should learn/work with CPLDs instead. However as far as I can see, CPLDs are much more expensive ICs than simple GALs (and a simple GAL is enough for me!) also I couldn't find hobby friendly DIP packaged CPLDs within the price boundaries about the same as common GAL devices (I would be OK with GALs with about max of 22 pins, no need - yet! - for fancy things requiring >40 pins with hard-to-deal-with packages and/or SMT). Eg "GAL 20 V 8 B-25LP LATTICE DIP24" costs less than $2 in a local store here in Hungary, but what rings the bells that they have limited storage on GALs and they said they can't get more later it seems as no longer produced ICs we're talking about.

Of course at the other hand someone can ask me why using 65xx when there are much more "modern" CPUs so maybe it's OK with stick on GALs too, just while 65xx is still actively produced, GALs are not, at this is my view now after checking out some vendors.

At the other hand I've found things like "TIBPAL20R8-10CNT (TI) HIGH-PERFORM. HIGH-SPEED 10ns PLD. DIP-24(3#)" for literally only cents (about 5 Hungarian Forint .....), these are PALs. But I am even less familiar with these devices than GALs, maybe OTP stuffs and even more outdated devices than GALs. But so cheap that maybe it's OK to throw them away and begin with a new one instead of reprogramming

It's true, those of us who like through-hole parts running at 5V are running out of willing suppliers. Those PALs look interesting - they are available in 5V through-hole and not too expensive. (http://www.digikey.co.uk/product-detail ... -ND/380730)

Most of here like the 6502 for reasons of nostalgia, or even first love. It's true that it's still produced and so there must be some commercial use of it, but by far the most use is embedded in a system on chip, probably in a toy. It's a simple processor which makes it good as a learning platform: whether to learn programming or to learn digital electronics.

Cheers
Ed

Atmel sells EEPLD's. These are similar to the old GALs. See for instance the ATF22V10C, or the ATF16V8

GAL (Generic Array Logic) and PAL (Programmable Array Logic) are essentially trade names. There may be some minor differences in options between one vendor and another, otherwise there would be no benefit to buying from one versus another.

As Arlet has pointed out, EEPLD (Electrically Erasable Programmable Logic Device) is also another trade name for the same type of programmable logic devices as GALs and PALs. An ATF16V8 and a GAL20V8 are essentially the same device with some minor capacity differences. A little specmanship never hurt anyone; I always found that vendors would count the inputs, the outputs, and the feedbacks of these devices in slightly different ways to make themselves look better than their competition.

Even the Complex Programmable Logic Devices (CPLDs) from Xilinx, Altera, Lattice, Atmel, etc. are essentially the same. Their internal organization is the same as the original GAL/PALs in that they have an AND plane followed by an OR plane. CPLDs distinguish themselves from GALs/PALs in that they generally include additional logic to "share" product terms between cells and to expand the width of the OR term of a particular cell.

In recent years, CPLDs like the CoolRunner II family have attempted to implement logic structures reminiscent to the Programmable Logic Array (PLA). The PLA differs from the GAL/PAL logic structure in that the OR plane can connect to any and all of the product terms, the AND plane. To make the logic structure producible, GAL/PAL vendors generally limited the OR plane. Devices like the 20V8 generally have OR plane connections to the AND plane for each output cell that varies from 8 to 12 product terms. (This is one reason that counters, adders, etc., where the more significant bits require more product terms to implement, are implemented on the outside of the device.)

Your greatest issue will be programming them. By that I don't mean writing the desired logic equations in a format/syntax that can be used by a translator. I mean finding a device that can physically program the JEDEC fuse file into the devices. In many cases, the older GAL/PAL devices may require programming voltages greater than 12V. EEPLDs may only require logic level voltages. With the advent of EE and Flash devices, the need for complex device programmers supporting high voltage programming of fuses and EPROMs has essentially disappeared. I have one such device, but the manufacturer went out of business several years ago.

My suggestion to you is to look long and hard at the 5V CPLD families, because even though they are bigger and hard to find in through-hole packages, they are generally programmable using JTAG. Furthermore, they are supported by free programming software from the vendors.

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Michael A.

Surely, 6502 is preferred by myself because it was my first CPU, and for the fun of programming on low level + also I try to building system with 6502 from now So of course I see your point and also I agree with your opinion. However the situation is a bit more complicated with other parts needed, like GAL/etc, since I am not so bound in my heart to GAL/FPGA/anything (unlike with the 6502) just I may need them to make my life easier, that's all. Since I have never used any programmable device (let it be OTP or reprogrammable). These PALs are interesting, I can buy 100 ICs for about 3-4$ according to the price list of a local electronical store nearby. Maybe they have some left-over nobody is interested in it anymore

Maybe some PLCC sockets are not so bad idea, as (AFAK at least, I haven't checked it out yet throughfully) there are through-hole PLCC sockets (and if they are compatible with standard pref board pin assignment, what I miss is still the lack of willpower to try to design custom boards, eh ....). Well, if there are 5V CPLDs in PLCC package at all

Ah, Michael is right, of course: programming a GAL means having a programmer. Or possibly building one: I found GALBlast (Version 1.6, 2003-05-29) in some archives:
http://reocities.com/mwinterhoff/galblast.htm
http://www.oocities.org/mwinterhoff/galblast.htm

Some us here have had success with Xilinx 9572 and similar, socketed too, but they are no longer manufactured (http://www.digikey.co.uk/scripts/dksear ... -15TQG100C). Note that sockets cost something...

Cheers
Ed

Ed, what would be stopping the typical hobbyist from going to 3.3V devices ? The W65C02 device will run at that voltage, and I'm guessing most other logic is easier to get in 3.3V nowadays. And if you wanted to interface with 5V equipment, there are ways to convert the voltages without too much pain.

There are also the GOP modules from OHO: http://shop.trenz-electronic.de/catalog/default.php?cPath=1_48_137

Note that these are a lot more expensive than GAL/PAL/whatever, but they should be more future-proof.

... by which I mean that it should be easier to program one of these modules a few years down the road.

What's that?

_________________
Michael A.

Arlet: good point, it may be that all necessary devices already work at 3V, or can be made to.

Also, some of the 3V parts, like the XC9572XL are 5V tolerant, and many 5V devices will accept a 3V signal as a logic high, so you can hook these up without any kind of level translator. Also, for 3.3V -> 5V conversion, you can use a regular 5V buffer IC as long as you make sure the logic high threshold is less than 3V.

PLCC sockets are available in thru-hole, and they definitely go into standard perfboard with holes on .1" centers. The unfortunate thing is that the wire-wrap versions (like what is show below) have disappeared.

_________________
http://WilsonMinesCo.com/ lots of 6502 resources
The "second front page" is http://wilsonminesco.com/links.html .
What's an additional VIA among friends, anyhow?

RS have them, but they are not cheap: http://uk.rs-online.com/web/c/?searchTe ... ra=oss&r=t