Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!uunet!seismo!kitty!larry
From: larry@kitty.UUCP (Larry Lippman)
Newsgroups: sci.electronics
Subject: Re: modems
Message-ID: <1870@kitty.UUCP>
Date: Thu, 23-Jul-87 13:28:11 EDT
Article-I.D.: kitty.1870
Posted: Thu Jul 23 13:28:11 1987
Date-Received: Sat, 25-Jul-87 11:17:47 EDT
References: <426@uop.UUCP>
Organization: Recognition Research Corp., Clarence, NY
Lines: 32
Summary: Buy 'em - don't build 'em

In article <426@uop.UUCP>, robert@uop.UUCP (Robert McCaul--The Equalizer) writes:
> even with the prices plummeting, would it be cheaper to build a
> modem?

	It might be theoretically cheaper in component cost, but you would
spend a hell of a lot of time doing it.

> where would i go about getting parts?
> i have lots of chip catalogs that list such things as modem chips..

	Assuming that you want an "auto-dial" modem, there is much more to
the modem that the actual modem IC.  You need a DTMF or rotary-pulse dialer,
call progress tone detection, telephone line interface, and logic to handle
commands and do dialing.  This logic is much too complex to perform with
discrete components, so it requires a microprocessor - like an 8051.
	As an example, consider the Silicon Systems SSI-K212 modem IC.
This IC comes out with a microprocessor data bus interface - so it MUST
be used with a microprocessor.  While this IC has a built-in DTMF dialer
and call progress tone detector, it has no telephone line interface, and
still requires a rotary dial pulsing circuit.
	As I see it, writing the microprocessor code to make this IC
work is not a trivial task.  I would guess that you would require at
least 500 lines of 8051 code to emulate a Hayes modem command set.
	
> but would it really be worth it?

	In my opinion, no.

<>  Larry Lippman @ Recognition Research Corp., Clarence, New York
<>  UUCP:  {allegra|ames|boulder|decvax|rocksanne|watmath}!sunybcs!kitty!larry
<>  VOICE: 716/688-1231        {hplabs|ihnp4|mtune|seismo|utzoo}!/
<>  FAX:   716/741-9635 {G1,G2,G3 modes}    "Have you hugged your cat today?"