Newsgroups: comp.robotics
Path: brunix!uunet!snorkelwacker.mit.edu!news.media.mit.edu!fredm
From: fredm@media.mit.edu (Fred G Martin)
Subject: Re: miniboard pullup resistors
Message-ID: <1992Oct29.235826.23810@news.media.mit.edu>
Sender: news@news.media.mit.edu (USENET News System)
Organization: MIT Media Laboratory
References: <1992Oct29.144124.14912@newshub.ariel.yorku.ca>
Date: Thu, 29 Oct 1992 23:58:26 GMT
Lines: 15

In article <1992Oct29.144124.14912@newshub.ariel.yorku.ca>
cs911225@ariel.yorku.ca (KEN E WILLMOTT) writes: 

>I have been examinn the schematic of the miniboard, and have
>noticed that there are (47k ?) pullup resistors on the port E
>pins. A long trip through the HC11 book (Motorola's) convinced
>me that they are not necessary for CMOS input biasing.
>Why are they there?

Hi Ken.  The answer is this:  so that simple resistive sensors (e.g.,
photocells, thermistors, etc) can be wired to the Mini Board with a
simple two-wire connection---the built-in 47k pullups act as the upper
leg of a voltage divider configuration.

	-Fred
