TECHNICAL BULLETIN #128 - Rev 1.10 (8/30/96)

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TITLE   : Lines, Dots, & Dashes in the Fax: Reverse Bit Ordering
PRODUCT : Procomm Plus 4.x, 3.x
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Incorrect bit ordering will cause a fax to be received (or sent) as pages
of lines and dashes.  This document explains the problem and how to use
Procomm Plus' reverse bit order options to solve the problem.

RECOGNIZING REVERSED BIT ORDER: LINES, DOTS, & DASHES

If your fax appears as a set of horizontal lines, dots, and dashes, you
are probably experiencing a bit order problem.  Typically when there are
bit order problems, the fax will send or receive successfully, but the fax
image will be unreadable. The image to the right shows typical reversed
bit ordered text.

In addition to the horizontal lines pictured above, you might also
experience several vertical rows of "|   ||     | ||    |".

This problem should only occur when using Class 2 fax method.  If you
suspect a bit ordering problem, be sure to check which fax method you are
using by selecting Setup | System | Modem Connection | Fax Settings | General
and reading the Fax Class box in the center of the screen (the path for
PROCOMM PLUS 3.0 is Setup | Fax | Fax Connection | General.)

WHAT CAUSES BIT ORDER PROBLEMS?

Bit order problems are the result of inconsistencies, among modem
manufacturers, in the methods used to implement Class 2 fax commands.
Your modem and computer exchange information one bit at a time.  When they
are exchanging fax image data,  the bits can be sent one of two ways:

   1.  Forward (first bit to last bit)
   2.  Reversed (last bit to first bit).

At the beginning of a Class 2 fax session, Procomm Plus sends a command to
the modem to send (or receive) fax image data to (and from) the computer
in forward order.

In some cases, modem manufacturers have reversed the commands.  This means
that the Procomm Plus command for forward bit ordering is the modem's
command for reverse bit ordering, and vice-versa.  In these cases we can
solve the problem using our Reverse fax bit order option.

In some other cases, our commands for forward and reverse bit ordering are
not the modem's at all, so using the Reverse fax bit order option has no
effect.  In these cases, we can reverse the bit order in the software
using the Reverse serial port bit order option.

FIXING BIT ORDER PROBLEMS: CHANGING YOUR SETUP OPTIONS

On the Menu Bar click Setup | System | Modem Connection | Fax Settings |
Advanced (in PROCOMM PLUS 3.0 click Setup | Fax | Fax Connection | Advanced.)

There are four check boxes relating to Bit Ordering.  Two are for Reverse
serial port bit order and two are for Reverse fax bit order.  Since the modem
commands for bit order during send and during receive are different, we have a
send and receive version of each option.

Each checkbox had three possible states.  Gray is the default value, and
means Use Procomm Plus' stored configuration for that modem.  In the majority
of cases this is correct.  For situations when it is not correct: a blank box
means Use forward bit ordering, while a checked box means Use reverse bit
ordering.

When resolving a bit order problem:

   1.  Change the Reverse fax bit order rate during send or receive
       (whichever you are having trouble with) option to its checked
       state.

   2.  Click OK in the lower left-hand corner.

   3.  Send a fax or have one sent to you.

   4.  If the problem continues, change the appropriate Reverse fax bit order  
       rate option to its unchecked (white) state.

   5.  Click OK in the lower left-hand corner.

   6.  Send a fax or have one sent to you.

   7.  If you are still experiencing the problem, repeat steps 1 through
       6, this time using the Reverse serial port bit order rate option.

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           Copyright (c) 1996 Quarterdeck  All rights reserved.
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