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PALs and 2023

SGarciaV

Hello all!

My first post in this forum. I haven't been to E14 in a while; now everything is different!

I may start a project in the near future that involves TTL 74LS logic. Currently, I will be using one 74LS00, but the chip count may rise depending on design decisions. A priority is keeping the chip count down, so I may want to integrate some of the glue logic. Way back - in the 80s -  I used PALs for this purpose. Doing some research, I see that this option is still available. Since we have fast-forward a few decades since the 80s, I am wondering if there is a more modern, mainstream option, other than PALs (or GALs).

This forum was the closest I could find to programmable logic, I hope it is the correct place to ask. I should mention that if my needs are simple enough a 16L8 PAL might do the trick (sorry, trying to remember this from back then). I have a TL866 II Plus, so if the device can be programmed with this programmer, it would be a plus. Thanks for any orientation or feedback. Salvador

  • in reply to shabaz

    Yes, it would be a personal project. In the short run, I want to recreate Grant Searle's 6809 computer (http://searle.x10host.com/6809/Simple6809.html). In the future, I would like to expand it. I like working with retro electronics because there is nothing I can do with modern electronics, at least with the equipment and skills that I have. I can still make use of my 100MHz oscilloscope when this old tech ran on 4 - 8 MHz.

    You present a lot of options, although I am looking to keep it simple. I estimate that at most, I'll have to implement various Boolean equations for decoding. I am hoping to reduce the chip count for glue logic to one chip (if possible). Currently, the above mentioned computer uses one 74LS00. Thanks for you r input, greatly appreciated.

  • in reply to dang74

    Yup, GALs and PALs have been on my mind. As other recommended, I am going to look at Microchip to see what they have to offer.

  • in reply to SGarciaV

    The fourth video in that blog shows how you can create logic circuits just by dragging logic gates onto a schematic page. No programming necessary. I think it is the easiest way to implement logic and it is very low cost. You could also easily implement more complex circuits by dragging peripheral function blocks into the schematic - such as UARTS, or if you want to generate a clock at a specific frequency - just type in the value to a clock module. (a simple way to test your 6809 running at different clock frequencies) It could probably even act as the RAM for your project although the part I used only has 2K or 4K.

  • in reply to SGarciaV

    IMO implementing a microprocessor is more a job for an FPGA than a bunch of CPLDs.  With an FPGA, you get in a single chip a large breadboard's worth of LSTTL parts plus the interconnect plus (usually) some SRAM.

    The downside of FPGAs is that they have a very steep learning curve -- I call it the Cliffs of Insanity.  I was lucky and started with FPGAs when they were still simple and rode the complexity wave up rather than trying to jump in later.  For someone starting with FPGAs, I highly recommend the Lattice iCE40 parts.  They have a simple 4-input Look-Up Table, plus adder logic, plus a modest amount of on-chip RAM.  They also give you the choice of free commercial tools from Lattice or open-source tools.

    shabaz mentioned the Lattice iCEstick, which is a nice board though overpriced IMO.  I see that Joel's Compendium of Cheap FPGA boards is still being maintained: www.joelw.id.au/.../CheapFPGADevelopmentBoards

    My favorite FPGA family is the still the Xilinx Spartan 3A, which had some wonderful boards back in the day.  Some might still be findable. I've done a lot of design with the Xilinx Spartan 6, but it's a very complex part.  Just groking the clock architecture is a big job.  So start with the iCE40 -- it's a nice clean architecture.