Re: [CAD_CAM_EDM_DRO] RE: PC based CNC system architecture

I think the use of USB is a reasonable solution. It is true that
transactions occur at 1 msec. rates, however, that does not mean it takes
one more millisecond to get a reply from a device.

If separate Bulk Pipes are used for input and output, you can post a read on
the In Pipe before sending data on the Out Pipe. As soon as the device is
ready to reply to the data sent on the Out Pipe, the reply will be sent
within the same 1 msec USB frame.

Also, USB 2.0 has been approved and early hardware is starting to appear.
USB 2.0 runs at 480 Mbps as opposed to 12 Mbps for USB 1.0 and 1.1.

There are USB engines available that include an 8052 type processor. The
one I have worked with in the past was from AnchorChips (which I think was
purchased by Cypress). One nice feature of this part is that the Windows
Device Driver can download the microcode for the device. This makes it very
easy to do software updates of the microcode.

I currently support Ethernet devices based on a 16 bit Kawasaki LSI device
(www.klsi.com) that has the same microcode download capability. All of the
device microcode is contained within the Device Driver and downloaded when
the device is connected.

John

----- Original Message -----
From: Steve Stallings <stevesng@...>
To: <CAD_CAM_EDM_DRO@egroups.com>
Sent: Saturday, December 09, 2000 8:41 AM
Subject: [CAD_CAM_EDM_DRO] RE: PC based CNC system architecture


> ..... further discussion about "black box" and the EPP interface
>
> >
> > Date: Sat, 09 Dec 2000 02:37:58 -0500
> > From: Matt Shaver <mshaver@...>
> > Subject: Re: Re: PC based CNC system architecture
> >
> <major snip>
> >
> >At this point we spent quite some time researching how to connect the
> >controller to the PC. I read most of the USB spec and concluded that
> it
> >wasn't feasible since USB devices can only start data transfers at
> 1ms
> >intervals. The data rate is high, but sending a command and receiving
> a
> >reply would take 2ms minimum due to the way the bus works. I'm still
> not
> >sure whether this is built in to the USB hardware. If anyone knows
> the
> >USB interface at the hardware level, I'd like to hear your thoughts
> on
> >this. Another problem with USB is that someone will inevitably plug
> >something else into the bus and goof everything up.
> >
> <more stuff snipped>
>
>
> About a year ago when Matt was starting down this path, I had a
> discussion with him about possible interfaces including USB. At
> the time I shared his misgivings about USB, but I am starting to
> come around. I have participated in two USB designs and now have
> a lot more faith in it.
>
> The 1 millisecond interval is definitely real, but as I understand it
> most current EMC implementations use 1 millisecond updates. While this
> is a lower limit to response time on USB, the latency can be made very
> stable. We have succeeded in transferring digitized voice over USB.
> In the case of an intelligent device such as Ron Ginger is proposing,
> the update speed is much less critical.
>
> The goof it up situation is getting better, but will probably always
> exist. On the other hand, who in their right mind would be fiddling
> with the USB bus on a machine controller. Set it up, test it, and
> leave it alone.
>
> Curiosity aroused.... I will investigate further.
>
> Regards,
> Steve Stallings
>
>
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