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From: elg@killer.Dallas.TX.US (Eric Green)
Newsgroups: comp.sys.cbm
Subject: Re: rs-232 interface for c64 (AN UPDATE !!)
Message-ID: <8096@killer.Dallas.TX.US>
Date: 13 May 89 18:32:57 GMT
References: <2502@csd4.milw.wisc.edu>
Organization: The Unix(R) Connection, Dallas, Texas
Lines: 35

in article <2502@csd4.milw.wisc.edu>, jgreco@csd4.milw.wisc.edu (Joe Greco) says:
> Anybody wanting to design a *cheap* RS232 interface should be using
> the MAX232 chip, which is no big secret.  I believe Steve Ciarcia
> outlined it's use a few years ago.  It generates the needed voltages
> from a single +5v supply, and should be a snap to use.

The company that my brother works for, SolaCom/CSI, makes modems
amongst other things (specialty modems for RF communications, but,
still, modems). They're using the MAX232 chip for the design they're
currently working on, which consists of an entire remote telemetry
unit stuffed into a 6-inch-square space. If they didn't have those
space limitations, they'd be using the old-fashioned 1488/1489 pair.
Reason? In quantity 100, they can get the 1488/1489 for around 50c
apiece. One 1488 and one 1489 are necessary. The MAX232 chip, on
the other hand, is close to $2 apiece in that low of a quantity (and,
mail order, the cheapest I've seen them is around $3-$4). Mail order,
I can get 1488s and 1489s for 65c apiece, and the circuitry to feed
them +/-10v (or nearbouts) consists of a couple of diodes and a couple
of capacitors, for a total cost of maybe 50c.  Note that you need two
MAX chips for a complete RS232 interface, so you have a cost of $1.50
vs. a cost of $5. That's at least a $10 difference in retail price
(and probably closer to $15). You won't sell a interface based around
the MAX chip for $28, that's fer sure....

Moral of the story: "New and improved" doesn't necessarily mean
"cost-effective". The MAX chip is cost-effective in the absense of a
rectifiable 9vAC power source... power supplies cost money. But on the
C-64, where you can readily obtain the voltages necessary, it just
don't make sense.

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