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

Chapter 8 171
Intrinsics Reference
FCONTROL(12, 13)
FCONTROL(12, 13)
Parameters
controlcode 12 — Enables character echoing.
13 — Disables character echoing.
param 16-bit unsigned integer by reference
(required)
Returns a value indicating the previous echo status to
the program.
0 = Echo ON
1 = Echo OFF
Notes FCONTROL with a controlcode value of 12 or 13
specifies whether or not input echo is enabled at a
terminal. Use 12 to turn echo on, 13 to turn echo off.
You may also need to use FSETMODE(4), to suppress
linefeed on inputs, to turn echo completely off.
When echo is enabled, all characters transmitted to the
DTC are “echoed” back and appear on the terminal
screen. This is referred to as DTC echo, and is initially
enabled for all terminals when the MPE/iX system is
brought up. All characters are echoed, with the
exception of XON, XOFF, NULL, DEL, and DC2.
During binary reads, however, all characters, including
XON and XOFF, are passed through as data. Since
these characters are not recognized and acted upon as
protocol characters, they will be echoed. An XOFF will
result in the terminal being suspended as if the XOFF
had been sent from the DTC. For this reason, you
should make sure that echo is disabled while in binary
mode. (An alternative is to disable XON/XOFF flow
control at the terminal, but this could result in a loss of
data.)
Echo should also be disabled during block mode
processing, and local echo should be used to cause the
terminal itself to write data to the screen. If you are
using VPLUS for your block mode applications, this is
handled for you automatically. For any other type of
block mode, you need to disable echo before the block
mode read begins.