You know how can write program for PAL/GAL?

Yes, you can use a few different tools, but I've had a look at WinCUPL. The code for the address decode is --

Thanks! It looks very simple, great!
I think the Spectrum Emulator card can be very reduced with GALs

You can probably use your eprom programmer to program the PAL.

Yes, my program can program PAL/GAL. (It is also, old but works under W7 x64, I just put a PCI LPT card to my PC )

I found some time last night to do the schematic and PCB layout for a 512KB SRAM expansion using a PAL for address decoding. It's come out really nicely -- less than 5cm square. Which means I can get it fabricated extra cheaply in China!

I was going to wait until I got my PCB's back from my HDMI project, but I may just go ahead and order these as well now, as it's only going to cost something like £12 to get 10 boards made.

PCB mock-up below!

Very Nice.......

I agree with Zozo that it would be good to see if the Spectrum Emulator can be
addressed in the same way.....

Russ

I've been thinking about the SD card <> PIC interface and a 5v tolerant CPLD (the Altera MAX 3000A is my preference) is by far the easiest and cheapest way of doing it. I believe the spectrum emulator would be the same solution, it would all fit in one CPLD.

You may even be able to fit a spectrum emulator into the CPLD with the PIC interface, as I dont believe it's very complicated!

If you want to use a CPLD maybe it should be considered to implement a general SPI interface in CPLD without the help of an MCU at all. Well it sounds odd, but somehow I always feel it's a bit cheating like action to connect an MCU to a 8 bit machine having more powerless CPU than the MCU itself ... The only disadvantage of this is the fact that you have to implement SD card init sequence and handling by Z80 code itself, directly. But it's a more "the EP is the boss" feeling then By the way, for 65xx bus system there is an existing "product" for creating an SPI interface "chip" with the help of CPLD with a Xilinx part (xc9572), the name of the project is 65SPI. Similar solution can be created for the EP bus too. Of course, if you have spare gates available, you can implement extra stuffs as well, like logic of a Spectrum emulator, etc

I also wanted to create an SD-interface solution with the help of an MCU (AVR, not PIC, but it's matter of personal taste and knowledge only). I would prefer CPLD (for various reasions including the feeling of using an MCU with a 8 bit computer, as I've told), the only problem that I am totally dumb for programming hardware decription lanugages (ie VHDL and/or Verilog) while I can write code for AVR at least using both of C or AVR assembly ...

I've ordered a batch of 10 pcb's now, for the bargain price of under £10.

Where you order?

I have placed a couple of orders with :

http://www.tinyosshop.com/

I haven't had any boards through yet, so I don't know the quality, but I've seen quite a few good comments about them on the web. For the price I figured it was worth a go. It works out cheaper than making the boards myself, and you get through hole plating and solder mask! Plus it means I can do vias under SMD components which makes life a lot easier.