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Backdoor Reference Manual - Version 1.0








Intrinsic Computer Systems
29 Ridge Road
Oak Ridge, NJ 07438
(201) 697 - 0174



















2
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LICENSE


All versions of Intrinsic's Backdoor are not public
domain software, nor are they free software.


Backdoor is copyright (C) 1988,1989 by Intrinsic
Computer Systems

Non-registered users are granted a limited license to use
Backdoor on a trial basis for the purpose of determining
whether the program is suitable for their needs. Use of
Backdoor, except for this limited purpose, requires
registration. Use of non-registered copies of Backdoor
by any person, business, corporation, governmental agency
or other entity institution is strictly forbidden.

Registration permits a user the license to use Backdoor.
A registered user may use the program on a different
computer, but may not use the program on more than one
computer at the same time.

No user may modify Backdoor in any way,including but not
limited to decompiling, disassembling or otherwise
reverse engineering the program.

All users are granted a limited license to copy Backdoor
only for the trial use of others subject to the above
limitations, and also the following:

Backdoor must be copied in unmodified form,complete with the
file containing this license information.

Any and all Backdoor documentation must be included with the
copy. No fee, charge or other compensation above a nominal
distribution charge may be accepted or requested. If any
distribution fee is charged it must not exceed $5 per disk.

Backdoor may not be distributed in conjunction with any
other product.

3
Operators of electronic bulletin board systems (Sysops)
may post Backdoor for downloading by their users only as
long as the above conditions are met.

Distributors of public domain or user supported
software may distribute copies of Backdoor subject to the
above conditions only after obtaining written permission
from Intrinsic Computer Systems. Such permission usually is
granted. Please write or call for details.

See the Ordering section for more information on
registration, corporate licensing and similar topics.
4

WARRANTY

Intrinsic Computer Systems makes no warranty of any
kind, express or implied, including without limitation,
any warranties of merchantability and/or fitness for a
particular purpose. Intrinsic Computer Systems shall not
be liable for any damages, whether direct, indirect,
special or consequential arising from a failure of this
program to operate in the manner desired by the user.
Intrinsic Computer Systems shall not be liable for any
damage to data or property which may be caused directly or
indirectly by use of the program.

IN NO EVENT WILL Intrinsic Computer Systems BE LIABLE TO
YOU FOR ANY DAMAGES, INCLUDING ANY LOST PROFITS, LOST
SAVINGS OR OTHER INCIDENTAL OR CONSEQUENTIAL DAMAGES
ARISING OUT OF YOUR USE OR INABILITY TO USE THE PROGRAM,
OR FOR ANY CLAIM BY ANY OTHER PARTY.
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6
L---+---T1----+-T--2----T----3--T-+----4T---+---T5----+-T--6----R----7--T-+---
CHAPTER Quick Start

Welcome to Backdoor. To allow you to install Backdoor as quickly
as possible, simply follow the directions below. If you feel,
after reading them, that you need more detailed instructions then
turn to Detailed Installation Directions. This will lead you
through the installation in a more thorough manner.


Step 1: Install Backdoor onto your hard disk into the
subdirectory you wish to keep Backdoor in.

b) Copy the files from the Backdoor diskette into the
Backdoor subdirectory:

copy a:Backdoor.*

Step 2: Run Backdoor

a) Type

Backdoor

Step 3: Press the key labeled "Alt" and the "h"
simultaneously. These are the Backdoor hot key
combination.

Step 4: Review the hardware settings for Backdoor.

a) Use the down arrow key to move the highlighted
cursor bar to "Hardware Setup" and press the
return key.

b) Look at the hardware settings presented. Make
sure your modem is connected to the
communications port number ("Com Port") as
displayed. Also, verify the baud rate,data
bits,parity, and stop bits.

c) If you need to change one of the hardware
settings, press the down arrow key to move the
7
cursor bar between the various hardware settings.
When the setting you wish to change is
highlighted, press the return key and enter the
correct hardware setting. Finish entering your
change by pressing the return key.

d) To save the configuration, press the ESC key to
exit to the main menu. Move the cursor bar to
"Config Save" and press the return key. The
hardware configuration will be saved.

Step 5: Explore! Call up the other windows and see how they
work.

Some Hints:

a) At any of the menus in Backdoor you can obtain
help by pressing the F1 key. A help window will
pop up to explain the various options available
to you.

b) When the main menu displays you may go directly
to a selection by pressing the first letter of
the selection.
8
CHAPTER Introduction

Thanks for purchasing Backdoor! Backdoor is a file transfer and
terminal emulation program. It works with Hayes compatible
modems and supports three widely used file transfer protocols
(Xmodem, Kermit, and Ymodem). It supports baud rates of up to
19,200. It has an ANSI compatible terminal emulator.

Backdoor will automatically schedule file transfers to other
Backdoor'd computer systems. You can set up Backdoor to answer
your phone and receive a file in the file transfer protocol of
your choice. It also, has an extensive logging facility.

It does all the above while you may be running,say, any
spreadsheet or word-processing package. While running your other
application, you may optionally have Backdoor inform you progress
of file transfer or you may directly call backdoor up to use
Backdoor's other features directly.

The rest of this manual is divided into sections which describes
each of these features as available from the main menu of
Backdoor. Once Backdoor's installed its main menu may be called
up by pressing the "hot key" combination. The default hot key
combination is "alt h."

If you have any comments concerning Backdoor they would be
greatly appreciated and can be sent to us via the above address
or via CompuServe. Our CompuServe identification number is
[75036,1602]. Please let us know what you are doing with
Backdoor, what applications, what hardware, etc. The better we
know you the better we can tailor our product to your needs.
Drop us a line with a return address, phone number, business
card, and brief description.
9
CHAPTER Transfer Status Window

This window's used to see the statistics of the current file
transfer and do some infrequent Backdoor operations. From this
window you may cancel the current transfer, toggle the top of
screen status bar, and remove Backdoor.

The Transfer Statistics Displayed are:

File Name: Contains the current file name being sent or
received. If no file is transferring then this field will
be blank

Bytes Xfrd: Contains the accumulated bytes transferred for the
current file. If the current protocol is Kermit this
byte count will accumulate to a larger number than the
actual file size. This is because Kermit uses a special
encoding scheme that translates binary characters into
two ASCII characters.

Last Msg: May contain a text message describing the last error
condition that has occurred. Depending on the nature of
the message the error my mean the current transfer is in
the process of aborting, or merely that a minor error
occurred and an attempt has or will be made to recover.
The list of error messages and their probable cause and
meaning is in the appendix.

File Xfrd so far: This field has the accumulated count since
Backdoor has started of files transferred.

File Xfrd since last check: This field has the accumulated
count since you last called up this menu of files
transferred.

Actions you may do while viewing this window.

Cancel Xfer: By entering a 'Y' in this field you will force
Backdoor to cancel the current file transfer. Press the
return, then press the 'Y' key. If you wish to escape
without entering a 'Y', either press the 'N' key or press
10
the ESC key.

Remove Backdoor: By entering a 'Y' into this field you will
force Backdoor to attempt to remove itself from the
computers memory. You may wish to do this before running
large application programs or programs that may conflict
with Backdoor. Please note that you cannot remove
Backdoor from memory if it's not the last installed TSR,
nor can you remove Backdoor if you are running an
application program.

To remove Backdoor move the highlighted arrows to this
field and press the return key. Then press the 'Y' key.
If you wish to escape without entering 'Y', either
press the 'N' key or press the ESC key. If you enter 'Y'
Backdoor will display a warning window. This warning
window will prompt you to press a key. Once you press a
key,if Backdoor can remove itself it will remove
its windows, if not it will display an error message.

Status Bar: By entering a 'Y' into this field you will allow a
status bar to display at the top of the screen. This
status bar shows the current file name transferring, the
number of bytes transferred, a status code (see
appendix), and the protocol in use. If you enter a 'N'
into this field the status bar will not display.

To change the status bar display status move the
highlighted arrows to this field and press the return
key. Then press the 'Y' or 'N' depending if want a status
bar or not. If you wish to escape without changing the
current setting either press the 'N' key or press the ESC
key.
11
CHAPTER Misc Setup Window

This window's used to set your autoanswer protocol type, the
directory to place received files into, the directory from which
files to send out from, and the key combination to start up
Backdoor. You may wonder why the send/receive directories must
be specified. The reason is, that since Backdoor is running in
the background while an application is active, the current
directory may be changed without Backdoor noticing it. If the
current directory changes Backdoor may lose a file its in the
process of transferring. Therefore, a fixed directory must be
used by Backdoor.


A change to the hot key field does not come into effect unless
you save the current configuration (See Main Menu Save Config
choice). The other fields changes do not become permanent unless
you save the current configuration, but they do become the
current until you remove Backdoor or reboot your computer.


The Misc Setup Fields are:

Receive Directory: This field shows the current directory that
will receive files. To change the directory, move the
highlighted arrows to this field and press the return
key. Then enter the directory name that you wish to use
for received files. If while entering the directory
name you wish to escape without changing the current
setting press the ESC key. When you do enter a directory
name Backdoor will check to see if the directory exists.
If it doesn't Backdoor will present an error window
informing you of this. Protocol: This field shows the
current default protocols for receiving a file. To change
the default protocol move the highlighted arrows to this
field and press the return key. Then enter the protocol
name that you wish to use for received files. You may
use the up/down arrow keys to have Backdoor present the
different protocols available if you choose.

If while entering the default protocol you wish to
12
escape without changing the current setting press the ESC
key. When you do enter a directory name Backdoor will
check to see if the protocol is a valid one. If it isn't
Backdoor will present an error window informing you of
this, and revert to using the previous entry of this
field.

Send Directory: This field shows the current directory that
will be used to send files. To change the directory, move
the highlighted arrows to this field and press the return
key. Then enter the directory name that you wish to use
for sending files.

If while entering the directory name you wish to escape
without changing the current setting press the ESC key.
When you do enter a directory name Backdoor will check to
see if the directory exists. If it doesn't Backdoor will
present an error window informing you of this, and revert
to using the previous entry of this field.


Hot Key: This is really two fields. You can use this field to

change the hot key combination that will start Backdoor.
This may be needed if Backdoor's hot key combination
conflicts with other TSR programs. Once this field
changed, the hot key combination will not come into
effect until you save the current configuration, remove
Backdoor and restart it.

To change the hot key combination, move the highlighted
arrows to either one of these fields and press the return
key. You may use the up/down arrow keys to have Backdoor
present the different hot keys available. Or you may
enter directly in the hot key name that you wish to use
for starting Backdoor.
13
CHAPTER Upload Setup Window

In this window you set up for files to be automatically uploaded
to other computers using Backdoor. In each row of this window you
enter the date/time, the telephone number to call, the
communications settings, and the filename to send.

In this window by pressing the down arrow key the highlight
arrows will highlight the entire row. If you press the down arrow
until the highlight bar reaches the bottom of the window and
continue to press down, more rows will scroll up. To modify
fields within a row press the right arrow, or the return key.
Then move the highlight arrow to the field you wish to change.

The Upload Setup Fields are:

Date: This is actually three fields next to each other. The
fields are in month,day, and year order. To change the
date, move the highlighted arrows to either one of these
fields and press the return key. Enter directly in the
number you wish to use.

When you do enter a date Backdoor will check to see if
the date is in the future. If it isn't Backdoor will
present an error window informing you of this, and revert
to using the previous entry of this field.

Time: This is actually two fields next to each other. The

fields are in hour - minute order. To change the time,
move the highlighted arrows to either one of these fields
and press the return key. Enter directly in the number
you wish to use.

When you do enter a time Backdoor will check to see if
the time is in the future. If it isn't Backdoor will
present an error window informing you of this, and revert
to using the previous entry of this field.

Baud: In this field you put in the baud rate of the receiving
computer. Please note that your modem must also support
this baud rate. Most modems support a range of baud
14
rates, and most will automatically adjust downward to the
incoming modem's. You must enter the baud rate that will
be used during the transfer of files, not the baud rate
the other computer will 'answer' at.

To change the baud rate move the highlighted arrows to
either one of these fields and press the return key. You
may use the up/down arrow keys to have Backdoor present
the different baud rates available. Or,you may enter
directly in the number you wish to use. If while entering
the number you wish to escape without changing the
current setting press the ESC key. When you are finish
entering the baud rate press the return key.

When you do enter a baud rate Backdoor will check to see
if the baud rate is valid. If it isn't Backdoor will
present an error window informing you of this, and revert
to using the previous entry of this field.

D, P, & S fields: These fields are the Data Bits, Parity, and
Stop bit fields. Usually, these are 8,N, & 1. However,
some computer systems set them differently so be safe and
ask.

To change the these fields move the highlighted arrows to
either one of these fields and press the return key. You
may use the up/down arrow keys to have Backdoor present
the different possible field contents available. Or,you
may enter directly the text you wish to use. If while
entering you wish to escape without changing the current
setting press the ESC key. When you are finish entering
press the return key.

Protocol: In this field you enter the file transfer protocol to
use to send the file. To change the protocol, move the
highlighted arrows to this field and press the return
key. Then enter the protocol name that you wish to use.
15
You may use the up/down arrow keys to have Backdoor
present the different protocols available if you choose.

If while entering the protocol you wish to escape
without changing the current setting press the ESC key.
When you do enter a protocol name Backdoor will check to
see if the protocol is a valid one. If it isn't Backdoor

will present an error window informing you of this, and
revert to using the previous entry of this field.

Telephone #: In this field you enter the telephone number of
the other Backdoor computer. To change the telephone
number, move the highlighted arrows to this field and
press the return key. Then enter the telephone number
that you wish to use.

If while entering the telephone number you wish to
escape without changing the current setting press the ESC
key.

Filename: In this field you enter the filename to send to the
other Backdoor computer. To change the filename, move the
highlighted arrows to this field and press the return
key. Then enter the file name you wish to send. If while
entering the filename you wish to escape without changing
the current setting press the ESC key.
16
CHAPTER Hardware Setup Window

In this window you set up the hardware settings for your
communications port. The communications port is how the IBM PC
talks to your modem. Your modem is how your computer interfaces
to the telephone system and finally to the other computer.

The Hardware Setup Fields are:

Com Port: The communication port is usually 1 or 2. If you have
an internal modem the port the port number must still be
set as the modem itself looks like a port to Backdoor.

Baud Rate: The baud rate field should match the baud rate of
the modem you will be using. Usually, this will be 2400
baud. However, baud rates from 300 to 19,200 baud are
supported. The faster the baud rate the more pauses you
will notice during a file transfer since Backdoor is
working with a higher volume of data.

Data Bits: This field is usually 8 and refers to the number
of bits per character of data sent over the serial port
or modem. The reason you may wish to change this is that
this setting should match the data bits of the modem or
computer system you will be connecting to. Some systems
use 7 data bits. To be absolutely sure of what the data
bits are, ask the owner of the other system.


Parity:This field refers to weather if any modem error
detection is done. There is no real standard setting for
this. It is possible to connect to another computer at a
different parity setting but usually the file transfer
will not work.

Stop Bits: This field is usually 1 and refers to the number
of bits that indicate the end of a character.

17
Modem Init String: The modem initialization string usually
begins with "AT." The actual string depends on the modem
type. Backdoor, supports Hayes or Hayes-compatible
modems only. Fortunately, most intelligent modems are
Hayes compatible. If you are using the modem at home the
string should be ATD. The "AT" is the modem attention
string, the "D" is the modem dial command. Backdoor uses
this string to issue dial commands to the modem.

If you are using this on a telephone system where you
need to dial a number to get to an outside line the modem
string should look something like this "ATD9." Where the
digit "9" would be replaced by the actual number you need
to dial out with. If you intend to only dial long
distance numbers then you may append the digit one onto
modem string. If you wish to dial long distance and
local numbers do not put in the long distance
prefix in this field. Prefix all your telephones (in
other Backdoor fields) with a one.
18
CHAPTER Config Save Window

Choosing this option will save the current configuration. The
current configuration is :

Dial Number (As used in Terminal Mode)
Hardware Settings (Defined in Hardware Setup)
Hot Key Combination (Defined in Miscellaneous Setup)

Modem Init String (Defined in Hardware Setup)
Protocol (Defined in Miscellaneous Setup)
Receive Directory (Defined in Miscellaneous Setup)
Send Directory (Defined in Miscellaneous Setup)
Status Bar (Y/N) (As defined in Transfer Status)
19
CHAPTER Save Schedule Window

When this option's selected the current schedule as setup in
upload setup is saved. Next time Backdoor is loaded it will load
in the schedule. If the scheduled has any files scheduled for a
future time Backdoor will send them at the scheduled time.
20
CHAPTER Review Log Window

When this option's selected you may review Backdoor's log file.
This log file contains status messages written by Backdoor. Each
message is date and time stamped so you can see when the message
was written. To review the file, simply press any key and it
will scroll through the log file. Press the ESC key to exit.


Messages are written on the following condition.

Abort of a file transfer
End of a file transfer
Start up of a file transfer
Time Out
Unable to open file
21
CHAPTER Virtual Terminal Window

When this choice's selected a partial screen virtual terminal
will appear. This terminal emulation is a subset of an ANSI
terminal. It supports simple cursor movement, line and screen
clears.

The terminal mode is usually a window that you can "pop"up on the
screen that will act like a "dumb" terminal. Characters received
during terminal mode while the terminal window is not up are
saved in an internal buffer. So, when you call up the terminal
window you will see the characters received since you last looked
at the terminal window.

One important note about terminal mode is that upon calling up
the virtual terminal you remain in terminal mode until the hang-
up key is pressed. Even if you exit, the virtual terminal (Alt-
x) you will be still in terminal mode. If you are in terminal
mode you cannot automatically receive file transfers from other
Backdoor systems - you must press the hang-up key combinations
(Alt-h).

While in terminal mode the following special keys are defined:

Key Description

Alt-d Dial a number
Alt-e Echo characters
Alt-g Capture screen
Alt-h Hang-up phone
Alt-k Script invocation
Alt-p Change port settings
Alt-x Exit

While in terminal mode you may start a file transfer by pressing
the PAGE UP or PAGE DOWN keys for sending or receiving.


Press the Alt-X key combination to exit the terminal mode.


22
Press the Alt-G key combination to capture a copy of the terminal
screen to a Backdoor.SCR file.


Press the Alt-P key combination to change the current port or its
settings (baud rate, parity, etc.).

To have Backdoor "echo" characters as typed in, press Alt-E
combination.

To dial out press the Alt-D combination and enter the telephone
number to dial, or on a Hayes' compatible modem type ATDXXXXXXX
where X is the telephone number.

To hang-up and exit the terminal into modem mode, press Alt-H.
Hanging-up is the only way to exit from the terminal mode into
the modem mode.


Alt-k is used to start a script file up. Type in the full name
of the script file including extension. To abort or exit a script
file, press the ESC key. Script file commands are described in
the appendix.
23
CHAPTER How To Set Up For Autoanswer

When Backdoor is loaded it automatically sets up the modem for
autoanswer. Then Backdoor goes into "Modem" mode. You can see
what mode Backdoor is in by looking at the status bar. When
Backdoor is in modem mode it will continuously wait for a
character to be received on the port. Once it detects a
character it will go into the default receive protocols' receive
sequence. For Xmodem this means, that Backdoor will start
sending a NAK character.

When in modem mode Backdoor will wait for the telephone to ring
(assuming you have a modem), and then enter into receiving a file
when the other system "connects" with your modem.

Warning! When you start up the virtual terminal from the menu,
Backdoor exits the modem mode and enters the "terminal" mode. To
restore the modem mode from the terminal mode, simply hangup
(alt-h) will in the virtual terminal. Backdoor will change the
mode to modem.

The reason the modem mode is lost once you enter the terminal
mode is that once you enter the terminal you may wish to maintain
it in that mode( even if you resume working on your foreground
application). Backdoor has no way of "knowing" what your
intentions are and therefor we designed it such that you have to
explicitly tell Backdoor.
24
CHAPTER Detailed Installation Directions


These detailed instructions are for installing Backdoor onto your
hard disk.

Step 1: Boot up your computer:


Step 2: Next at the DOS prompt create the Backdoor
subdirectory on your hard disk. The Backdoor
subdirectory name may be of your own choosing or
even an existing one. However, we recommend that
Backdoor be put in its own subdirectory if for no
other reason but to keep it separate. Once you
choose where in your hard disk's directory structure
to put the new directory, move to its parent's
directory via DOS's CD command and use the following
DOS command to create the new directory:

mkdir Backdoor

Step 3: Next move to the new directory by typing:

cd Backdoor

Step 4: Copy the files from the Backdoor diskette (we assume
its in the A drive) into the Backdoor subdirectory
by typing the following command:

copy a:Backdoor.*

Step 5: To Run Backdoor type:

Backdoor
25
APPENDIX

How Backdoor Works

Backdoor belongs to a class of programs called "Terminate and
Stay Resident (TSR)". It installs itself and becomes part of
your computers, memory - not permanently though!

Backdoor works in the "background" while another program is
working in the "foreground." This "background/foreground" stuff
merely means that while a program you are using is running,
Backdoor is periodically run.

Backdoor, when it does run, usually runs for only a few tenths of
a second. However, depending on such things a whether you're
doing a file transfer, how fast your disk and computer are,
Backdoor will consume more time. This may be as much as a few
seconds.

During these occasions the computer may appear to pause. Don't
worry! Backdoor is merely do something in the "background" and
will return the computer to the "foreground" application as
quickly as possible.
26
APPENDIX Scripting

Scripting's intended to allow you to create script files for
automated sign on to the remote systems that you use. To create a
script file use your word processor (in its straight ASCII mode)
or EDLIN (comes with DOS).

Script file commands are very simple and will work in 95% of all
cases. The commands may be upper or lower case, and may have
leading white space. You may also have blank lines.

The commands are as follows:

WAITFOR "XXXXXXXXXXXXXXXXXXXXXXX"

Where "XXXXX..." is the string to wait for. Control characters
are denoted by preceding them by the caret '^' symbol. For
example to wait for "USERNAME:" where there is a carriage return
after the user name string use the following:

WAITFOR "USERNAME:^M"

Please note the quotes around user name are part of the syntax of
WAITFOR and must be included. If part of the string you wish to
wait for has a double quote character then put two double quotes
in the string.

WAIT NNNN

Waits for NNNN seconds. Pauses execution of a script file for
NNNN seconds. You cannot escape from this command. This command
is useful in situations where a pause may occur on the other
system. You therefore may wish to wait for a few seconds.

As an example to wait for 300 seconds (5 minutes) the command
would be:

WAIT 300


27
SEND "XXXXXXXXXXXXXXXX..........X"

This command sends the string "XXXXXXXXXXX...X" to the remote
string. The string may contain control characters as the WAITFOR
string can. As an example to send a password sign on the
following might be sent:

SEND "YOURNAME^N"


DIAL NNNNNNNNNNN

This command dials the number NNNNNNN. Note the NNNNN number may
contain commas or dashes. For example to dial the long distance
number 201-430-7700 the following would be used:

DIAL 1-201-430-7700


#

This command simply allows comments be inserted in your script
files. Any text on the same line, following the pound sign will
be ignored.
28
APPENDIX Error Codes and Messages

The following is a list of the possible error numbers that will
appear on the top of screen bar, and the corresponding error
message in the status window. Under each message is a brief
explanation of what it means and possible causes and corrective
actions (if necessary).

Error Message


1 Record header mismatch


During a file transfer the header of a packet had a
mismatched sequence number.


2 CRC error


During a file transfer the CRC check failed for a
packet.


3 Buffer full


During a file transfer the internal buffer of Backdoor
filled up. This means that Backdoor didn't have a chance
to empty its buffer to disk. A possible reason is that
the foreground program was doing extensive disk activity
(such as formatting a disk). Or that the directory that
Backdoor puts it files to is full or inaccessible (does
Backdoor think its directory is on a floppy which is no
longer in the floppy?)


4 Buffer empty



29

5 Invalid record header


During a file transfer a packet was received with an
invalid record header.


6 Time out


During a file transfer the other side failed to send a
recognizable packet or did not send any packet at all
during a fixed period.


7 Xfer aborted by other end


During a file transfer the transfer was aborted by the
other computer. This may have occurred because of the
other side not having enough disk space or by the other
sides operator.


8 Can't open file - Fatal


During a file transfer Backdoor was unable to open the
file it was to send or unable to open the file it was
creating( during a receive).


9 Can't write file - Fatal


During a file receive Backdoor was unable to write to the
file. This may be because of the disk is full or Backdoor
is unable to access the file (floppy door open?).

30

10 Port hardware error


This occurs when a parity error, overrun, or framing
error's detected on the port. Corrective action is
sometimes unnecessary since errors due occur on telephone
lines. If this error is recurring rapidly such as
several times a second, then probably your port hardware
settings (or the other computers) is incorrect.


11 Invalid packet type - Fatal


During a file transfer (usually a Kermit transfer) a
packet was received whose packet type wasn't expected.
This usually suggests a severe synchronization problem
exists between the two computers and therefor is
irrecoverable. Backdoor will send an abort file transfer
to the other computer.


12 Unable to synch up - Fatal


At the beginning of a file transfer Backdoor was unable
to start the exchange of file packets.


13 Record out of sequence - Fatal


During a file transfer Backdoor got a packet with a
sequence number out of order. This usually suggests a
severe synchronization problem exists between the two
computers and therefor is irrecoverable. Backdoor will
send an abort file transfer to the other computer.

31

14 Communication Interrupt Stolen


When Backdoor starts up it re-vectors the communications
ports interrupt to itself. If while Backdoor is in the
background another communication program is run in the
foreground, the foreground program will re-vector the
communications interrupt to itself. Backdoor will detect
this and while the foreground communications program is
actively using the communications interrupt Backdoor will
do nothing (other than show this error code). After the
foreground program releases the communications interrupt,
Backdoor will re-vector the interrupt to itself.


15 Transferred OK


At the end of a successful file transfer, Backdoor will
show this message.


16 Packet Resent


If during a file transfer a minor error's detected, the
usual course of action is to resend the packet.