Newsgroups: comp.robotics
Path: brunix!uunet!think.com!enterpoop.mit.edu!news.media.mit.edu!fredm
From: fredm@media.mit.edu (Fred G Martin)
Subject: Re: 6.270 Boards -- be careful before deciding
Message-ID: <1993Jan17.222345.26639@news.media.mit.edu>
Keywords: control robot miniboard pcb 6.270
Sender: news@news.media.mit.edu (USENET News System)
Organization: MIT Media Laboratory
References: <1993Jan17.075322.10766@magnus.acs.ohio-state.edu> <1jc2p1INN903@life.ai.mit.edu>
Date: Sun, 17 Jan 1993 22:23:45 GMT
Lines: 37

In article <1jc2p1INN903@life.ai.mit.edu>
anarch@cookie-monster.ai.mit.edu (Anne R Wright) writes: 

>All revisions of the 6.270 board that we have tested -- version 
>2.0, 2.1, and 2.2 -- all fail when using the Motorola 68HC11A1 
>chips currently available.  6.270 has traditionally used A0 rather
>than A1 chips and they work fine.  However, the new chips will 
>frequently enter an illegal state on reset which causes the 
>6811 to corrupt its own memory.

Anne, ave you tried using one of Motorola's low-voltage reset chips
tied to the RESET line?

(The reset chip is a 3-wire device packaged like a TO-92 transistor.
It has power, ground, and output.  The output is low (causing the
uproc to be in the reset state) until the power level rises above 4.5
volts.)

I'd be willing to wager that this would solve the problem easily.  I
forget the part number offhand, but it's a pretty neat little device,
and it would be trivial to hack it into an existing board.


>The board will have to be partially redesigned in order to 
>smoothly incorporate debouncing circuitry, if indeed that is 
>the entire problem, and there are no plans right now to do 
>this.

Since the board designs may be distributed freely, net readers should
know that they are free to download the board design and make the
changes themselves---there's no reason the net community has to wait
for MIT people to fix it.


Cheers,
Fred

