Newsgroups: comp.robotics
Path: brunix!sgiblab!swrinde!cs.utexas.edu!utnut!torn!newshub.ccs.yorku.ca!newshub.ariel.yorku.ca!cs911225
From: cs911225@ariel.yorku.ca (KEN E WILLMOTT)
Subject: Re: HC11 board design
Message-ID: <1993Sep20.143023.6542@newshub.ariel.yorku.ca>
Keywords: HC11 CMOS pullup
Sender: news@newshub.ariel.yorku.ca (USENET News System)
Organization: York University, Toronto, Canada
References: <1993Sep19.135642.22263@newshub.ariel.yorku.ca> <CDLxvr.Etv@news.claremont.edu> <93262.131906LEEK@QUCDN.QueensU.CA>
Date: Mon, 20 Sep 1993 14:30:23 GMT
Lines: 30

Although CMOS inputs may *happen* to float high/low is
no guarantee that they will continue to do so, upon
chip/factory-die/weather/temperature/phase of the moon
changes.

There is a "clean" way to eliminate a lot of the pullup
resistors from the basic single chip circuit of the HC11.
Just configure them as output pins in your startup code.

This strategy would leave them floating for only a few
microseconds, every time a reset or power  up occurs.
It is highly unlikely that any damage could occur in
this brief time.

The only pins that cannot be so modified are:

	IC1
	IC2
	IC3
	STRA
	IRQ
	XIRQ
	MODB


Of course, if you're using the A/D, you need one on VRH.
The 10M across the xtal goes without saying.

	-Ken Willmott

