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First CPLD project

Hi All,

I'm doing an internal project for my tiny company and have chosen to use a Xilinx XC9572 and an Atmel ATMEGA324P along with 6 74LS245 transceivers for this portion.

This project is a board to interface to an ancient (but initially very expensive) machine, replacing the original interface with a modern one. The original is all 5V and I don't care about speed, density, power consumption or cost too much. I'm mostly interested in ease of implementation and reliability.

Anyway, I bought a Xilinx USB II cable the other day and was looking for any pointers or tips you may have.

I have both Windows XP SP3 and Ubuntu 8.04 available for development. I'd prefer to do most or all work under Ubuntu. Is that practical using the Xilinx toolset?

I am currently working on the schematic/board for the above and plan on clocking both the CPLD and uP at 20MHz. Any thoughts on the necessity of using a four-layer board (inner layers power/ground)?

The basic function of the CPLD will be to accept byte-wide writes to one of 16 possible registers from the "ancient machine" (Intel 8085 @3.0 MHz.) and to store this in the CPLD as a 12 bit value, possibly double-buffered, then to interrupt the uP. The uP will read and decode the 12 bit value from the CPLD and store the 8 bit part in RAM. Going in the other direction the uP will write to a single 8 bit wide register, possibly double-buffered, in the CPLD which will cause the CPLD to issue an interrupt to the "ancient machine". Sometime later the "ancient machine" will read the register in the CPLD and the CPLD will clear the interrupt line.

Back in '86-'88 I got fairly proficient with 22V10s and ABEL. I haven't done any programmable logic since then.

Later in this project I'll be using a mid-sized FPGA (probably Spartan

3) to implement some faster and more complex logic (specialized 20 Mbps data stream organized in scan lines)

Thanks.

Reply to
gregben
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I can do XC9572XL development 100% on Linux (Fedora 6) so you shouldn't have a problem with that. I don't use the USB cable, though, I made my own programmer from a spare MCU and the XAPP058 sample program. I can program an XC9572XL in about 12 seconds with it.

Reply to
DJ Delorie

You didn't mention the package you're using for the XC9572, but in any case 4 layers is probably worth the peace of mind. 2-layer boards need very careful attention to ground and power routing, and remember that even such a venerable part as the XC9572 (not -XL?) still has fairly fast edge rates and flip-flops fast enough to clock on reflections.

If I'm not mistaken, you can still program the XC9572 in ABEL with the Xilinx webpack tools, but don't quote me on it. However if you plan to move to a small FPGA for the next version I would recommend learning either Verilog or VHDL. The schematic entry tools from Xilinx are not ready for prime time IMHO.

At 20 MHz, I would suggest looking at Spartan 2 or Spartan 2e to save possible headaches with power supplies. The last time I checked the Spartan 2e was still the cheapest device per user I/O (but not per fabric LUT or flip-flop). What you lose in the Spartan 2 series is the DDR I/O flip-flops and DCM (Digital Clock Manager) but they still have DLL's (delay-locked loops) if you need something simple like a clock doubler.

Another cheap source for small to medium FPGA's is the Lattice ECP2 series. These are more along the lines of Spartan 3 feature-wise.

With a somewhat larger than minimum-size FPGA in the newer series you should be able to embed a small processor and get rid of your "ancient" CPU as well.

Regards, Gabor

Reply to
Gabor

We have used the "Platform USB" cable and the Parallel port CABLE IV from Xilinx under Redhat EL4 using the impact software. (You need root PW to install the parallel port drivers and I believe the kernel source installed)

The Digilentinc parallel cable also seems to work with impact under EL4. This cable comes with the Digilent Coolrunner CPLD development board. (Remember your PC needs a parallel port for this, many new laptops dropped the PP)

Reply to
Nitro

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