Configuring Systems for Terminals, Printers, and Other Serial Devices (32022-90057)

Describing Asynchronous Devices
How to Control Printers
Chapter 9
181
Vertical Format Control
Many printers use Vertical Format Control (VFC) to direct the placement of output. VFC
instructs a printer to skip to predetermined lines or to a specific point on a page with
typically one or two commands, instead of counting and outputting a number of blank
lines and spaces. This capability is often referred to as “Skip to Channel x,” where x is
one of the predetermined points.
Printer Initialization
When a printer is shared, each user can manipulate the printer in a different way. One
user can change the printer’s characteristics (such as margins, tabs, or print density) and
affect another who does not want those characteristics.
To prevent one user from affecting other users, the printer must be initialized to a known
state before printing the next job. When a printer configured as printer type file 21, 22,
or 26 is opened, the ASC software writes an initialization character string to the printer.
Printers using printer type file 18 cannot use the initialization string. This means that if
a user changes the printer’s characteristics, the characteristics are not reset by the ASC
software. The user’s program must reset the printer when it is finished with it.