Serial, parallel, SCSI, and Local Talk are all ports that
the printer manufacturer adds to the laser engine. The video
port is already present. Some printer manufacturers do not
present this video interface to the outside world; some
do. If the video interface is activated by a circuit board
inside the PC, but outside the laser printer, this device
can disable temporarily the computer developed by the printer
manufacturer. The printer manufacturer's serial and parallel
ports are essentially put off-line while the video interface
is controlled by the device external to the printer.
Suppose that a Hewlett-Packard LaserJet II is hooked to
a serial PC, parallel PC, and video PC printer controller.
These three PCs are going to share the one laser printer
without any added software or a LAN. Suppose that the video-connected
PC is not printing anything. Then, the parallel or serial
PC will have control over the printer. You can switch the
parallel and serial PCs by using the front panel of the
PC. The video PC printer controller is actually connected
to the laser engine. When the video-connected PC starts
to print, it disables the Hewlett-Packard serial or parallel
port until it is done. In other words, the video PC printer
controller will share with the parallel PC or serial PC
automatically. You must switch manually the parallel and
serial PCs.
Unfortunately, the video PC printer controller cannot take
advantage of any of the features of the Hewlett-Packard.
The video PC printer controller uses only the engine of
the Hewlett-Packard. The video PC can send instructions
only to the Hewlett-Packard part of the laser printer.
SCSI cables have terminators similar to the floppy and
hard disk drives inside IBM PCs. You should have one T-resistor
plugged into the SCSI device at the end of the cable. If
you plug in two T-resistors, premature hardware death will
occur. If you do not plug in any T-resistors, many soft
errors and data damage will occur.
The official Apple cables for hooking a LaserWriter to
a Macintosh are very expensive. As a result, many people
purchase the cables from a company called Farallon. Farallon
uses regular telephone cables.
