Asynchronous Serial Communications Programmer's Reference Manual (32022-90052)

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6 Typeahead Mode
Effective with Release A.20.00, a typeahead capability is supported for
use on MPE/iX systems. Typeahead makes it possible for a user at a
terminal to enter data before the read which will accept that data is
actually posted. This is especially convenient when you need to enter a
series of commands with system processing delays in between.
The typeahead facility is controlled programmatically through the
FDEVICECONTROL intrinsic, using one of three control directives.
This chapter explains each of these typeahead controls, and provides
code samples demonstrating how you can do the following:
• Control whether or not typeahead is enabled at a terminal.
• Bypass the typeahead buffer and take data for the next read directly
from a terminal device.
• Flush all information from the typeahead buffer before starting the
next read.
NOTE DTC Telnet typeahead is operational only when single echo is enabled.
Use FDEVICECONTROL with controlcode value 192 and parm1
value 63, or the TTUTIL program, to enable single echo. PAD
typeahead is operational only when initial echo is disabled. Use
FDEVICECONTROL with controlcode value 192 and parm1 value 4,
FCONTROL(13), or the TTUTIL program to disable initial echo.