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From: kjh@pollux.usc.edu (Kenneth J. Hendrickson)
Newsgroups: comp.dcom.modems
Subject: Practical Peripherals 9600 SA
Message-ID: <28692@usc>
Date: 8 Dec 90 11:47:46 GMT
Sender: news@usc
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Long, but informative discourse on Practical Peripherals 9600SA modem
follows:  (includes nasty [and greatly detailed] bug reports)

After a recent call to my friendly (yeah, right) system operator, I
decided to try something on my PPI 9600SA modem.  By changing some S
register settings, I was finally able to connect at 2400 and 1200!

Before you call me a BONEHEAD, read on . . .

I gave the command "at &q0" to disable all error correction, because the
1200 and 2400 bps modems that I was calling don't support error
correction.  Voila, my 9600 bps modem that never worked before at 1200
or 2400 bps now works just fine!  But wait, the problem is not solved.

When I call a modem that doesn't have error correction, and I have the
registers set as follows: s36=5 or s36=7, s48=128; the feature
negotiation SHOULD be disabled - immediate fallback to the setting in
s36 SHOULD occur.  This setting for s36 indicates that MNP2-4 SHOULD be
attempted, and if this fails either a standard asynchronous (direct
mode) connection SHOULD occur for s36=5, or a (normal mode) connection
with ASB automatic speed buffering SHOULD occur for s36=7.  (This is all
assuming that the &q setting is &q5.  It was.)

THE ABOVE DOESN'T HAPPEN.  Upon connection, the light for error
correction is lit, even though the answering modem doesn't have error
correction.  This indicates that the Practical Peripherals 9600SA modem
has defective control software.  The modem spits out terrible noise for
10-15 seconds, and then finally looses the connection.  The PPI firmware
authors are the BONEHEADS, and not I.

In addition, I found some more bugs/features.  If you give the command
"at &q0" followed by "at &q5", or "at &q8" followed by "at &q5", the
values of the s36 and s48 registers will be set to 7, regardless of what
was previously set in them.  I think this is a bug.  Maybe PPI thinks it
is a feature.  In any case, you must give a separate command AFTER
"at &q5" to set the s36 and s48 registers as desired.

There is another bug.  This cannot possibly be construed as a feature,
no matter how hard you try.  If you give "at &q0", or "at &q8", followed
by "at &q5", YOU WILL NEVER AGAIN ACHIEVE A CONNECTION WITH ERROR
CORRECTION OR DATA COMPRESSION OF ANY TYPE.  It doesn't matter what the
settings in the relevant S registers are.  You have to cycle the power,
if you ever want to get a connection with EC or DC again.

There is yet another bug.  Again, the modem just doesn't work as
advertised.  If you give "at &q8 s46=136" you SHOULD get a MNP 2-4
connection.  If you give "at &q8 s48=138" you SHOULD get a MNP 5
connection.  In fact, you don't get either.  I was calling a modem that
had MNP5, and the connection would be made WITHOUT ERROR CORRECTION (to
say nothing about data compression).  You can work around this one, by
first giving "at &q5", and then "at s36=7 s46=136 s48=13?".  However,
there is no excuse that I will accept for "at &q8" not working as
advertised.

The good news is that my testing and evaluation has led me to believe
that the filtering, modulation, and demodulation functions of the PPI
9600SA modem work well.  They appear to work well at 1200, 2400, and
9600 bps speeds.  The bad news is that the control software in the
modem really sucks; it is full of bugs.

I heard a rumor about a new software version, 1.18, from PPI.  I don't
know what bugs this revision will correct.  I don't know if I should
take another chance.  If the PPI software engineers were boneheads, and
didn't correct these bugs, how can I trust that the next firmware will be
any better.  If the PPI testing department engineers didn't find the
bugs, and are thus boneheads, how can I trust that they will find the
bugs in the next version to be released.  If the PPI marketing
deptartment is staffed by boneheads, and says "ship it", even with the
bugs, how can I trust that PPI will ever ship a quality product?

I want the price of a PPI modem, but I also want quality.  I guess I am
willing to pay for quality.  If I ever find it, I'll get on here and
recommend it.

In the meantime, I must recommend AGAINST the PPI 9600SA.

-- 
favourite oxymorons:   student athlete, military justice, mercy killing
Ken Hendrickson N8DGN/6       kjh@usc.edu      ...!uunet!usc!pollux!kjh