Newsgroups: comp.robotics
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From: kilian@cray.com (Alan Kilian)
Subject: Re: 68HC11EVBU fanout data
Message-ID: <1992Oct13.124859.5364@hemlock.cray.com>
Lines: 29
Nntp-Posting-Host: gopher
Organization: Cray Research, Inc.
Date: 13 Oct 92 12:48:59 CDT


I like Fred's method of connecting HC11s better than mine for all the reasons
he stated.

I got my idea from the way that Motorola uses the SPI interface on the
HC16 to connect to several LED device drivers. They are all connected
daisy chained and you send out a 24 byte packet to update all the LEDs
pretty much like that method for controlling many motors from one HC11
using shift register chips.

I have changed my mind and I like connecting all the MOSI MISO and SCK
pins together (You know what I mean) and have software deal with getting
the slaves to talk back to the master one at a time.

By the way there is also a slave-select pin *SS which will select which
slave will receive the data. You could use this pin on 8 slaves connected
to an 8 bit output port on the master and not bother any of the other 7
slaves from having to recieve the packet and then toss it if it is not for
them. It does take up an 8 bit port though but if your slaves are using
all their power to just keep up with their workload then this keeps them
from having to recieve packets and them throw them away. I doubt I'll need
to resort to this and I'll just have a header with a slave address.

-Alan "It's a man's right to change his mind until he gets a good one" Kilian

-- 
 -Alan Kilian           kilian@cray.com 612.683.5499 (Work) 612.721.3990 (Home)
  Cray Research, Inc.   655 F Lone Oak Drive, Eagan  MN, 55121 
                        "It's based on actual math". -Dilbert
