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

296 AppendixA
Comparing MPE/iX Systems to MPE V Systems
Software Characteristics
Using [Break] During Writes
Because of the speed with which MPE/iX systems process writes, more
data can be lost if
[Break] is entered while a program is writing to a
terminal than was the case for terminals connected to MPE V systems.
The Command Interpreter and [Break]
During a read in the MPE V CI, [Break] is disabled. It is not disabled in
the MPE/iX CI.
Preemptive Writes
With MPE V, a preemptive write can interrupt a read or another write.
With the ASC software on MPE/iX computers, a preemptive write will
interrupt a read or a write not yet started, not a write that has already
started.
During Reads. Suppose, you are using the CI to type in MPE V
commands on a terminal. You want to use the :SHOWJOB command and
begin typing. The system operator sends you a message with the :WARN
command after you have typed only the characters SH. The :WARN
message interrupts your read and is displayed on the screen. The SH
characters you have already entered are discarded, and a new DC1
character is sent to your terminal. You must begin typing the word
SHOWJOB again because the SH was lost when the read was preempted
by the message.
With MPE/iX, a :WARN message will interrupt the read as if it were a
:WARN message on MPE V. However, in the example above, when you
have typed SH of the :SHOWJOB command and receive a WARN message,
the SH is not lost, and no new DC1 character is issued. You need to type
only OWJOB to execute the command.
During Writes. On MPE/iX, a preemptive write will not interrupt
another write that has already started. Writes that have not yet started
will be delayed until after the preemptive write.
Logical Console Functionality
On all HP 3000 computers, terminals other than the system console can
temporarily obtain partial console functionality with the :CONSOLE
command. This is called moving the logical console to a terminal. MPE
V systems allow the logical console to receive console messages, execute
normal console commands, and execute console commands that require
the console attention character (
[CTRL]-A).
The functionality of the logical console on MPE/iX computers is the
same, with one exception: the logical console cannot execute console
commands that require
[CTRL]-A. The [CTRL]-A character is not