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From: akcs.jwtrav@hpcvbbs.UUCP (John Wettroth)
Newsgroups: comp.sys.handhelds
Subject: Re: 48SX: Hardware project to receive I/R I/O
Message-ID: <28040da5:2500.3comp.sys.handhelds;1@hpcvbbs.UUCP>
Date: 11 Apr 91 07:40:13 GMT
References: <1371@cameron.egr.duke.edu> <1570021@hpnmdla.hp.com>
Lines: 16

actually the last response is correct.  the ir is simple once you've got
a handle on it.  my real answer should have been that the ir consists of
52 microsecond pulses of light for logic ones but other than that is much
like the output of a standard uart.  a project for your vlsi class that
might be interesting and fun would be to make a "uart" that could receive
hp ir and stretch it to times that would be compatible with a standard
uart (like those in a pc).  the way this could work would be to have a
latch that would take the ir and get set and have a counter that would
come by every 420 microseconds (2400 baud) and sample it.  standard uarts
sample at the center of a bit period after getting sync'ed on the start
bit.  your uart would sample at the center but the input would be
latched.  this latch would be reset shortly after a sample for the next
sample.  do this 11 times and pass through the output, level shift with
something like a maxim max-232 chip and you would have rs-232 that could
go into a pc. this kind of stuff is easier to do with a micro-controller
using interupts but would be a good exercise for anyone. good luck and
thanks to the last responder for the clarification.