Re: servos

David Howland wrote:

> I have designed a digital PWM servo amplifier board. I am considering all cost effective computer interfacing means available so that I end up with a reasonable total cost for accomplishing what I set out to do.
>
> I have started a list of possible computer interfacing methods with costs. Obviously the overall system performance may be limited by the system architecture one selects, and worse, the programming and construction time may be a little demanding, however, TV is a real waste of time. The most scary fear I have is the compatibility with application programs, but it's all on paper for the moment.
>
> Computer Interfacing cards and aproximate price:
> ISA SCSI-II Controller card $50
> PCI USB I/O Card $40
> Dual port ISA Bi-directional Printer Card $35

USB is a real exciting option, but I wonder, how long does it take for a request from a R/T module to be sent
through the USB driver to the custom motion box, and then for a reply to come back through the driver to the
R/T module. Actually, that can't work, anyway. So, if the R/T module had the code to manage the USB,
then nobody else could use it. Maybe with that restriction that the USB couldn't be used for any other purpose,
maybe this would work.

Same problem, then, with the SCSI interface, it would have to be a private resource to the R/T code.

And, the printer interface is just too narrow (8 data bits plus way too few control lines) to be a good
data path. Also, there are limits on how many printer ports you can have (unless you hack the address
decoder).

Jon