Date: Wed, 29 Mar 2000 07:31:39 -500
From: Tom Rutherford <[EMAIL PROTECTED]>
Subject: Modem power considerations etc.
On 27th Mar 00 at 8.32pm, Nettamer List <[EMAIL PROTECTED]> wrote:
NL>Date: Mon, 27 Mar 2000 17:11:26 -0800 From: Mark Willis
NL><[EMAIL PROTECTED]> Subject: Modem power considerations
NL>etc.
NL>A while back, there was a post about modems and AC vs. DC
NL>power packs.
NL>Usually designers use a Maxim MAX232 or equivalent - that chip
NL>creates several needed voltages easily from the existing DC
NL>supply voltage, using switched capacitors, and translates TTL
NL>levels to RS-232 levels. Several other co's make that IC, as
NL>well. AC power packs are a little cheaper to make - you then
NL>have to put the same rectifier/capacitor parts inside the
NL>modem, instead of in the power pack, so it's just a costs
NL>trade-off thing. Which power pack can you get cheaper and
NL>reliably sourced, usually <G>
NL>COST of device components is probably THE major consideration
NL>in most consumer electronics - obviously, from watching the
NL>market, reliability / functionality come in second, fairly
NL>often =)
NL>RS-232 usually hangs out at some negative voltage between -5
NL>and -12V, and goes positive when characters are sent;
NL>Details on the MAX232 family at
NL>http://dbserv.maxim-ic.com/quick_view2.cfm?pdf_num=1798, you
NL>can grab a data sheet from there.
NL>(I've been catching up on things, busier than I'd like!)
Thanks, Mark. I'd forgotten about the negative voltages on the RS-232
interface, but they're there. I think there's a -5 and a -8, isn't
there? I know there's a couple, anyway, that aren't TTL compatible.
Most RS-232 ports are probably MOS these days, anyway, right? :-)
-- 73 DE Tom Rutherford, N8EUJ, Burton, MI
OXYMORON: Congressional ethics
NTReader v0.23(P)/Beta in conjunction with Net-Tamer
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