Ethernet medium can be in realtime take a look at sercos3 for example.
It uses standard ethernet hardware.
Sent on the TELUS Mobility network with BlackBerry
-----Original Message-----
From: "Mark Wendt (Contractor)" <mark.we...@nrl.navy.mil>
Date: Sun, 27 Feb 2011 11:10:15
To: Enhanced Machine Controller (EMC)<emc-users@lists.sourceforge.net>
Reply-To: "Enhanced Machine Controller \(EMC\)"
<emc-users@lists.sourceforge.net>
Subject: Re: [Emc-users] Guidance on usb comp
On 2/27/2011 8:03 AM, Peter Blodow wrote:
> Hello Mark,
>
> Ethernet is a sloppy name for IEEE 802.3, the real protocol name is
> Carrier Sense Multiple Access/Collision Detection (CSMA/CD). In local
> wireless networks, /CA is used (Collosion Avoidance) instead of /CD.
> Other Bus protocols are based on the same idea such as CAN bus (CSMA/CR,
> Collision Resolution) and others.
>
> All these protocols have in common that they are asynchronous and data
> transmission is randomly timed, depending on network load. Just the same
> especially with serial busses like USB.
>
> Since EMC is based on exactly timed pulse generation, there is
> PRINCIPALLY no use trying to adapt it to the protocol systems mentioned.
>
> Why not stick to the parallel port?
>
> Best regards
> Peter Blodow
Peter,
I work on a daily basis with Ethernet as a system and network
administrator.
We're talking about a Real Time Ethernet, with a dedicated master and
slave network interface, which should preclude any worry of collisions
on a duplex connection between the two. Modern systems with full duplex
connections no longer really rely on CSMA/CD. As defined in 802.3,
that's just one of the protocols that have been used, not the only way.
The reason we're talking about Ethernet as one of the possibilities for
communications between the computer and the controller is the
possibility of the ultimate demise of the parallel port, and the
difficulties of real time communications on the USB bus.
So, Real Time Ethernet ain't quite your Granddaddy's TCP/IP or USB
protocol. If it can be worked into a real time communication scheme,
unlike USB, it may be a possible alternative to the parallel port when
the parallel port is no longer supported. And, if it's a dedicated
port, like the parallel port is, and can be controlled by the Real Time
kernel, it can handle the timed pulses in 100 Mb, Gig E, or 10 Gig E
depending on the network interface that's supported by the software.
Mark
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