Re: Questions on Single Board Computers

[Mark Allyn <allyn@well.com>]

Nikolaus:

Thanks for the suggestion.

The DMX serial protocol that I am using uses a packet of 512 words
that it sends out at once. There is no need for an address field
as each packet sent out ever the line has all 512 words (8 bits each).

This is done to eliminate the need of having address bits. Each light
in a DMX system (which, by the way is used in most modern theatres
and concerts; especially the big rock concerts) is programmed to
use a particular byte of that 512 bytes.

The one thing that I did not mention in my email is that I am
hoping for a 512 KBPS bit stream on the line so that I can
update the brightness of each LED at least 60 times per second.
A 9600 baud line would be too slow.

Looking at the RS485 hardware specs, they say that it can run
up to 1 MBPS for the distances that I am looking at (up to about
2 meters for a piece of clothing). It also has a fan out limit
(transmitter to receivers) of about 32. That is show stopper
for me.

Perhaps I can make 'repeaters'; a RS488 receiver connected to a
RS488 transmitter on a small PCB. I was hoping to avoid this.

Truly,

Mark Allyn