S3Board

This board was officially called “Spartan-3 Starter Board”. It was sold directly by Xilinx, and also by Digilent, who made it and still sell it today. But accessories like the Module Interface Board that provides for easy PMOD connection are no longer available. The 200K gate S3Board was my first “real” FPGA board, and I started my first experiments with VHDL, and later also the PDP11 core on it – but the PDP11 grew out of the 200K gates quite quickly, so I upgraded to the 1000K gate version of the S3Board. Besides the usual connectors, buttons, leds and switches, the board has a nice big four-digit 7-segment display. Great for blinkenlights.

The S3B200 (called thus because of the gate count of the FPGA on the board) is really a bit too small for the current PDP11 model, I’m really only still including it for sentimental reasons – it was my first board, after all. It will just fit an 11/10, a single serial console, and a reduced RK11 controller with only two drives. Just enough to run RT-11 on, everything more complex or other controllers are beyond what the optimizers can do – or what I can do by reducing the core. Getting the core reduced to this point was an interesting exercise which took me a couple of days and provided a couple of very new insights into how the VHDL translation to hardware really works. But I don’t think I can take it any further, and the resulting model also is not always reliable as the optimizer needs to work quite aggressively to reach the target size. There is not even enough room left to run some blinkenlights – and that maybe really drives home the point that this board is too small. What is the purpose of a homebrew PDP11 without blinkenlights anyway?

Digilent still sells the upgrade 1000K variant of this board. It’s not really an interesting option anymore – Spartan-3 is becoming ancient technology, the chip is still somewhat smallish at 1000K gates, and the board is a bit too expensive for what it does, compared to the newer boards from both Digilent and Terasic. But, if you have one already, it can make for a nice 11/45 or even 11/70, for instance to run V7 Unix on.