fpga4fun.com

Hello. So let me start by saying that I was wonderfully happy to find this site! The examples are great. Some of the code is a little confusing with my rudimentary understanding of VHDL, but I'm working through it.

In particular, I was curious about using the servo-driving code to implement a servo controller on my FPGA board. I have the Xilinx Spartan 3E starter kit board.

I believe I have 48 usable I/O pins, so I'd like to see if it'd be possible to control a whopping 48 servos from this thing. I'll actually probably do less when I start using this as a robot controller, but I'd like to do a lot nonetheless.

Unfortunately I don't have all my hardware on hand, but I seem to remember that having 48 of the servo controller blocks would easily fit into the 500K gate fpga on my board.

The part that I am not sure about, being a neophyte in the ways of electrical engineering, is how to disburse the control of these motors. Ideally, I'd like to be able to control them from a PC, for now.
RS232 seems like it'd be too slow, I think ; 6 bits for a specific servo, then 12 bits for a position, sent in three bytes, for 48 servo's. At 11520 bps, That'd only allow me a position update very 12.5 ms, if I was moving all at once.

Maybe EPP? Someone should tell me how to do it with that....

Ideally, in the future, I'll have a much migher level control going to the board, and positions will be calculated internally, so I probably will have to get the PicoBlaze running.

Thanks,
Andrew

12.5 ms is faster than the servos update anyway unless you have some expensive special servos.

If the serial link is a problem you can send just the information needed and triple the speed or you can use faster RS-232 hardware up to 2 MBit/s.

Printer port is fast and simple but requires a driver unless you run from DOS or some old type OS that allow direct hardware access.

If you need a CPU anyway I don't see the need for the FPGA at all, it is just going to make everything ten times as expensive and complicated. A nice 32 bit microcontroller can do it fine.