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

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1 Introduction
The HP 3000 Series 900 computer supports a wide range of useful
peripheral devices. This manual describes how devices which are
connected to a DTC and communicate asynchronously (such as
terminals and serial printers) interact with the MPE/iX operating
system. It also describes how asynchronous devices can be controlled
programmatically through the use of system intrinsics. Only the subset
of intrinsics useful for control of asynchronous devices is described here.
For a complete listing of all the system intrinsics available with MPE/iX
see the MPE/iX Intrinsics Reference Manual.
When you are programmatically controlling devices connected to your
system, it is vital that you have a basic understanding of the way each
specific device interacts with the computer. How this interaction occurs
depends on such diverse factors as baud rate, transmission method and
the purpose for which the device is being used. In order for successful
communications to take place, the computer and the peripheral device
must agree on the method of communication being used and must know
exactly what to expect from each other.
This chapter provides an overview of how communications take place
between an MPE/iX system and the asynchronous serial devices
connected to it. The following topics are discussed:
• The types of devices that communicate in an asynchronous serial
fashion.
• The physical components of the Datacommunications and Terminal
Subsystem.
• The software that governs Asynchronous Serial Communications.
• The basic data communications concepts involved.