Configuring Systems for Terminals, Printers, and Other Serial Devices (32022-90051)

198 Chapter9
Describing Asynchronous Devices
How to Control Printers
How to Control Printers
Controlling printers is similar to controlling terminals, except for two
differences:
• Printers have no need for control mechanisms (such as echo, read
trigger, special characters, or modes of input) related to user input.
Note: printers which support status checking require a read trigger.
• Printers need additional control mechanisms to define how output
will appear on the printed page, as well as special ways to prevent
data loss.
Each of the methods for controlling printers is explained in the pages
that follow. Refer to the Asynchronous Serial Communications
Programmer’s Reference Manual for more information on programmatic
device control.
Transmission Speed
Asynchronous data transmission speeds on MPE/iX computers range
from 300 bps to 19200 bps. The following speeds are supported:
300, 1200, 2400, 4800, 9600, and 19200 bps. 38400 bps is also supported
for direct connect devices on DTC 16iX/16MX and DTC 72MX.
If host-based, transmission speed is configured through NMMGR. The
speed chosen must be supported by the printer. A printer can be
changed to any supported speed if it is directly connected to the DTC.
The speed of a printer connected to a modem is set by the speed of the
modem and the telephone line being used.
Parity
Parity verifies that each character of data is transmitted between the
system and the printer without error. It detects data transmission
errors, but does not correct them. Printers using printer type file 21 use
parity. Printer type file 21 generates odd parity. When a printer using
printer type file 21 encounters a parity error, it remembers the error
until the ASC software verifies the printer's status. When the error is
returned to the ASC software, a message is printed on the system
console.
Printers using printer type files 18 or 22 cannot use parity. Additionally,
the FCONTROL and the FDEVICECONTROL intrinsic cannot be used to
change the parity settings for printers. For more information on parity,
refer to “How to Control Terminals” earlier in this chapter.