From: davidg@aegis.or.jp (Dave McLane)
Newsgroups: comp.dcom.modems
Subject: Re: Digicom vs Supra - flames wanted
Date: 28 Jan 93 06:19:11 GMT

markp@cranham.cc.earlham.edu (Mark Pearson) writes:

>OK, we have decided to try out a Zyxel 1496 modem.
>Now for the comparison.
>I'm all for a Digicom Scout+. My boss is all for a Supra.
>The only major drawback to Digicom that I know of is that apparently if one  
>connects the telephone to the PHONE jack on the modem and the wall socket to  
>the LINE jack one cannot get the modem to dial a telephone number for one.
>Since I regularly use Info Select to dial my numbers and I need to have the  
>phone connected via the modem this is a major inconvenience. Any comments?

According to the manual this should be possible (see p 32
"Automatically Dialing a Voice Call") but when I did what it said,
it didn't work. The only way I was able to get it to work was to
dial out with "ATD{D|T}xxxxx ;", then pick up the handset, then
enter "ATH". No so good ... maybe somebody else a better solution.

>A major advantage has got to be responses via comp.dcom.modems. I don't see any  
>technical support for Supra modems that way.

It's one of the main reasons I went for Digicom; you can't dial 800
numbers from Japan. 

>Second question - there must be another!
>I have been following the threads about 16550AFN UARTs etc. Either I missed the  
>following or it wasn't said, but :

>At what baud does a 16550 become desireable?

I haven't had any luck with running UARTs less than a 16550AFN (or
integrated circuitry emulating such UARTs) at more than 9600 BPS. 

>For example, if you're using V32 & MNP 5 then your DTE speed might be 19,200. 
>Does this warrant a 16550? I guess that using V32 and V42.bis to give 38.4 Kb  
>would require it. We're talking here of a bog standard 16MHz 386sx machine.

IMHO there is only one way to know for sure and that's to set up the
modem and the software and try and send/receive a file and see if it
drops characters. I use two tests for this: One is with Z-modem as
it will show CRC errors. The other is to send/receive a file like this:

* 0001 TEST TEST TEST TEST TEST TEST TEST TEST TEST TEST TEST TEST *
* 0002 TEST TEST TEST TEST TEST TEST TEST TEST TEST TEST TEST TEST *
....
* 1000 TEST TEST TEST TEST TEST TEST TEST TEST TEST TEST TEST TEST *

Because the pattern is regular, it's easy to see if any characters
are missing even at 3,000 CPS. I've found that it's almost
impossible to upload a file like this with echo-back from a host as
the software can't keep up with both sending and receiving 3,000 CPS
in both directions even when the flow control is right and the chip
is a NS16550AFN. 

>I'm also confused conceptually about whether internal modems handle the data  
>stream differently from external ones. Any pointers?

I only use external modems as I have a variety of machines and like
to be able to move the modem from one to the other. It also makes it
easier to isolate the modem from the machine if there are problems.
I also like having add-on cards with socketed UARTS as this way I
know for 100% sure exactly what the chip is. 

Hope that helps,

Dave

--
Dave McLane 
JUNET: davidg@aegis.or.jp (ONLY within Japan: post otherwise)
Nagaokakyoshi, Kyoto Japan Tel: +81-75-951-1168 Fax: +81-75-957-1087
Newsgroups: comp.dcom.modems