Using PLC?

[Terry Sare]

     Umm, I am confuse here. The USB (Universal Serial Bus) is a point to 
     point, master - slave communication link between a host and endpoint. 
     That endpoint can be anything you wish it to be, mouse, keyboard, 
     speakers, etc. The micro that supports the USB link simply contains a 
     USB serial engine to handle the interface. The serial engine handles 
     two rates: 12mbits/sec high speed or 1.5mbits/sec.
     
     Something to consider:
     
     1. The host controls the link, currently Intel is the only real 
     producer of host interface chips as part of their PIC3/4 chipset. Not 
     real easy to use these thing. Software for interfacing to the host is 
     very slim pickens' and documentation of the host interface is poor. 
     There has been ads for other host controllers but most have been "real 
     soon now" (Netchip comes to mind cause I have their eval board).
     
     2. The link can support Isochronous, bulk, control, and interrupt 
     packets. Isochrounous has no error checking but is for audio, video, 
     etc. and a missing bit doesn't matter as much as on time delivery. 
     Transfer rates from the spec indicate 1mbyts/sec. Bulk has smaller 
     size, but has error checking built in. Rate is about 1Mbytes/sec. 
     Control and interrupt are what they say they are and not relevant to 
     moving data.
     
     3. The micro type limits the above mention transfer rates, the Intel 
     part only does about 600Kbytes/sec in bulk xfer, the Cyprus parts are 
     for keyboards and mouse. That is according to their ads :-). The only 
     way to achieve full speed is using an external SIE and a high speed 
     micro (x186,332, etc.).
     
     4. Unless you have software on your Wintel computer to support the USB 
     link, you have no way to use the USB link. Remember, it is point to 
     point, master slave. One USB device cannot talk to the other in peer 
     to peer link. At least, not if you follow the spec. :-).
     
     Now, if somebody has some software source for controlling the USB host 
     under DOS, I would love to see it. The USB is a nifty interface but 
     since W9x is required -- doesn't do much good for playing with.
     
     Ouch, can you say long winded!!! No, I do not design with USB. I just 
     have to deal with testing the host interface cause all of our 
     computers have them.
     
     BTW, skip firewire for now, the spec is not really stable, the parts 
     are not readily available, and what do you need a 100-400+mbit/sec 
     link in a car for :-) umm on second thought don't answer that. And 
     yes, I have seen firewire run and it is quick. 
     
     Terry Sare
     terry_sare at dell.com


______________________________ Reply Separator _________________________________
Subject: Re: Using PLC?
Author:  diy_efi-owner at esl.eng.ohio-state.edu at dell_unix
Date:    1/21/1998 8:55 PM

<snip>
jan 15 1998 EDN article on USB said only sustained rates of 6 Mbps 
which is same as a ECP parallel port. I would check out FireWire.
 Alex
snip
>
>                                    -Scott Flanagan     (flanagan at worldnet.att.
net)
<snip>> >
> >Matt Watts
> >University of Utah
> >Formula SAE Racing
> >_________________
>
>