Newsgroups: comp.robotics
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From: fredm@media.mit.edu (Fred G Martin)
Subject: Re: Powering up MiniBoard w/o chip?
Message-ID: <1992Dec8.154628.24575@news.media.mit.edu>
Sender: news@news.media.mit.edu (USENET News System)
Organization: MIT Media Laboratory
References: <1992Dec7.232514.4444@memstvx1.memst.edu>
Date: Tue, 8 Dec 1992 15:46:28 GMT
Lines: 21

In article <1992Dec7.232514.4444@memstvx1.memst.edu>
langston@memstvx1.memst.edu (Mark C. Langston) writes: 

[powered up his Mini Board w/o CPU]

>The result?  LEDs 6 and 9 lit up (the green LEDs for motors 1 and 4), and
>the red POWER LED barely lit up.  Is this normal, or should I be worried?
>I don't expect it to power up normally, but why is something like this
>happening?  Anyone know?

The red 'power' LED is connected to the TTL serial output bit of the
6811.  When the serial line is "resting" this bit is high, and the LED
is on.  When the CPU is in download mode, the serial line sends a
break character---the line is low, and the light is off.

The dimly lit state corresponds to either (a) no CPU present; or (b)
the output line in high impedence mode.  Look at the schematic and
you'll see the resistors causing the dimly lit state.

	- Fred

