|
PureBytes Links
Trading Reference Links
|
It seems impossible to say much of anything on this list without offending
someone and becoming the target of public or private insults. However, I
can't imagine who this will offend, so I will give it a try.
A printer port security block usually does not interfere with the operation
of a printer connected to the same port. Likewise, a printer usually does
not interfere with the operation of a security block. However, in some
cases either type of problem can occur.
Security blocks, like modems, have two modes of operation. There is a
normal mode where data is passed through. There also is a command mode
where it is not.
In the case of modems, the command mode is used to change communication
protocols, baud rates, the number of start and stop bits, and other things.
In the case of a security block, the command mode is used to activate a
block and ask it to identify itself, and in the case of a sophisticated
block, to ask it to encrypt or decrypt program files or data, or do other
things. Both with modems and security blocks, special signals are used to
switch between the normal and command modes. Both with modems and security
blocks, other signals sometimes are mistaken for the correct ones. If a
printer port security block mistakenly switches to command mode, it will
assume information sent to a printer is for it, so it won't pass it through
to a printer.
The signal mix-up most often occurs when a computer first boots. When
computers boot, the BIOS (Basic Input Output System) sends reset commands to
each serial and parallel data port to clear any error conditions and to
ready them for normal operation. That should cause no security block
problems, but some computer parallel port hardware sends a signal when it is
reset that is interpreted by security blocks as a signal to switch to
command mode. If that happens, a security block will "eat" everything sent
to a printer port afterward, so a printer connected to the same port will
receive nothing.
There are several solutions. Installing a different parallel port card in a
computer usually will correct that problem. Replacement parallel cards are
widely available for $10 to $20. They usually are easy to install.
Printer port security block manufacturers are continually designing-in new
filters to trap the invalid signals sent when some computers boot. If an
Omega security block doesn't work correctly with a printer on your computer,
Omega might be willing to exchange your block for a newer one that will work
with the computer parallel port hardware you already have. I have no idea
whether they will be willing to do that. I am only suggesting a solution
that likely would solve the problem.
The second type of problem is where a printer interferes with the operation
of a printer port security block. That problem is rare, although many
complain of it where the problem actually is the problem described above.
It doesn't occur with most printers, but there are a few printers on the
market that short parallel printer port data lines to ground when they are
switched off. A printer that does that will short-circuit communication
between a computer and a security block whenever the printer power is
switched off.
That problem is more difficult to overcome. The leading security block
manufacturers supply blocks that will work with those printers. The only
other easy fix is to disconnect the printer data cable from the security
block when the printer power is off.
-Bob Brickey
Scientific Approaches
sci@xxxxxxxxxx
|