ASCII printer and plotter links allow RSCS to send data streams
of ASCII characters and control sequences to ASCII printers and plotters.
These ASCII devices must be connected to the z/VM system
by an IBM 7171 ASCII Device Attachment Control Unit, 9370 ASCII Subsystem
Controller, or equivalent ASCII controller.
This link driver task is made up of routines
and exits in DMTAPT and customer-supplied ASCII exit routines. The
APT task uses the following exits to provide ASCII functional support
for printers. These exit points are called at various points in the
processing cycle of the driver.
INIT
Performs any required initialization
TAGEX
Processes TAG information
RECEIVE
Receives each spool file record
RESET
Resets the device after any logical end of a spool file
MSGEX
Translates messages into ASCII format
ATTNEX
Processes attention interrupts generated by the 7171 ASCII Device
Attachment Control Unit or 9370 ASCII Subsystem Controller
TERM
Called just before the link driver terminates.
As Figure 1 shows, each exit in DMTAPT corresponds to
an ASCII printer or plotter exit routine. These routines can customize
the way the ASCII-type link driver communicates
with a specific ASCII device. These exit routines can modify or translate
the input spool data. They can also add ASCII control sequences based
on the external characteristics of the spool file.
Figure 1. Structure of an ASCII-Type Link Driver
All calls to exit routines follow standard OS conventions. ASCII
exit routines must also follow these conventions when returning control
to DMTAPT. See z/VM: RSCS Networking Exit Customization for more information about ASCII exit
routines.
