Re: [CAD_CAM_EDM_DRO] Re: USB on Linux

Les Newell wrote:

> USB relies on having an intelligent peripheral on the end of the wire,
> unlike a 'dumb' parallel port. In this case it would make sense for the
> periperal to do the time-critical drive processing as well, removing the
> need for critical bus timing and drastically reducing bus traffic. As you
> have to have a processor of some sort in the peripheral it would not affect
> the price or complexity of the interface to do this.

That's another reason why I did my interface on the parallel port.
Although there is an incredibly complex protocol for intelligent devices
associated with IEEE-1284, you don't have to use it. I chose not
to incur all that overhead. I can use $6 CPLD logic chips (lower density
than a true FPGA) to handle the lower-level bus protocol and run
my DAC or digital I/O. For the encoder counter or stepper rate generator,
I needed to implement these more complex functions, so I put it all on
an $18 FPGA. With a processor, unless it is all integrated, you need
RAM, ROM, the peripheral function itself, the CPU, the bus interface,
etc.

Jon