PALs and 2023

Hi,

74LS is obsolete, there are other logic families that might suit you more. 

In any case, the (slightly more) modern replacement for typical PAL chips were CPLDs. They are also now not as common, but there are plenty for sale on Farnell/Newark, so if this is a hobby project, then CPLD could still be a suitable option. They are easy to use (either by using a more normal HDL (Hardware description language; like VHDL) than early programmable logic used (which were more like a text description of table entries), or by directly entering in logic gates into a schematic). 

A nice CPLD family is Xilinx Coolrunner, e.g. XC2C64A, there are hundreds of them in stock according to the Farnell site, and they cost about £10 each (not cheap, but for a hobby project there's often not a requirement for least cost). The required software is Xilinx WebPACK, which is still available from the manufacturer website. The chip comes in TQFP package, but some are very large (0.8mm pin spacing) and easy to solder onto a breakout board using a normal soldering iron. They can be programmed using (say) a raspberry pi, hooked up to the programming pins (called JTAG).

However, the next step up from CPLD is to use an FPGA. The easiest way to get going with them is to first buy a dev board since that may contain a programmer built-in, and easy to use connectors (most FPGAs are finer pitch parts than the old CPLDs), and then when you're happy, you could move to the individual IC. A lowish-cost dev board is ICE40HX1K-STICK-EVN (£49 GBP, currently 99 in stock on the Farnell website). The basic FPGAs such as that are not much harder to use than the CPLDs, but depending on the manufacturer free supplied software they might not come with a schematic entry method, you may have to use a HDL. There is also open source software but that's another topic altogether, and is not applicable for all HDLs. FPGAs take their configuration from external memory by the way, unlike CPLDs.

Yet another approach could be to consider something like Infineon/Cypress PSoC chips or dev boards, they are a microcontroller with a (very tiny) bit of programmable logic attached. However I know nothing about those, and cannot comment.

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.

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.

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.