Asynchronous Serial Communications

A terminal is a hardware device that enables an end user to communicate with the computer, and both send data to and receive data from the system. All terminals supported for use on MPE/iX systems include typewriter-like keyboards and CRT screens. Some personal computers capable of running in terminal emulation mode are also supported for asynchronous connection.

Terminal types are assigned to each terminal port configured for the system and serve to help define the terminal's features. For a complete discussion of terminal types see Configuring Systems for Terminals, Printers, and Other Serial Devices.

Like terminals, serial printers can be connected to the system using asynchronous serial communications. Unlike terminals, serial printers are used only to receive information and to transfer that information to paper in a permanent, readable format. Printer types are used to help define the characteristics of each serial printer port configured for the system. A complete discussion of printer types can be found in the Configuring Systems for Terminals, Printers, and Other Serial Devices manual.

Plotters are special graphic devices which allow you to transfer computer generated drawings to paper by plotting their X and Y coordinates and moving pens to corresponding locations on the output surface of the plotter.

In some cases asynchronous communications may take place over telecommunication lines. Because the signal used by computers (digital signal) is different from the signal transmitted over telephone lines (analog signal), a device called a modem is required on each end of such a link. The word "modem" comes from "modulator/demodulator", which describes the function of the device.

The system console is a terminal used by the system operator to execute specific tasks for the purpose of managing sessions, jobs, and system resources. A system console is connected to each HP 3000 Series 900 computer through a special access port, and system console functions are controlled through the Console Management software. Some of the console functionality can be temporarily transferred to another terminal, or logical console. This can be useful if it is necessary to receive console messages on another device. Most system control functions, however, cannot be executed from a logical console.

While the system console is technically an asynchronous serial device, its functionality, as well as its physical and logical interfaces, are very different from those discussed in this manual. For more information on the system console see Managing Peripherals manual.

Theoretically, any device that conforms to Hewlett-Packard's asynchronous protocols and is capable of being physically connected to the system can be controlled through Asynchronous Serial Communications. This could include test instruments, data collection devices, etc. Such devices must be capable of performing XON/XOFF flow control, and should be configured as terminal type 18 or printer type 18. Extreme care must be taken when connecting any non-supported device.

	NOTE: Non-HP devices are not supported. HP is not responsible for troubleshooting customer problems that involve the use of non-supported devices

The Telnet protocol provides a standard virtual terminal connection between the HP 3000 and other HP and non-HP systems. MPE/iX Telnet connections can be made using one of two solutions: 1) via a direct HP 3000 implementation called "Telnet/iX" which enables users to have direct access to, or from an HP 3000 using the Telnet protocol. This product provides both inbound and outbound Telnet connections using only HP 3000 resident code. 2) via a Datacommunications and Terminal Controller (DTC) with a Telnet Access Card (herein referred to as "DTC Telnet") which provides only inbound Telnet access to an HP 3000 through a DTC.

Telnet/iX provides the Telnet service over Transmission Control Protocol/Internet Protocol (TCP/IP) on MPE/iX. The Telnet/iX Client enables users on an HP 3000 to have direct access to HP 9000, HP 3000, and non-HP systems that support Telnet and TCP/IP. The Telnet/iX Server enables users on a remote system running standard Telnet services to logon and run most applications on the HP 3000. Many MPE/iX file system intrinsics are supported over Telnet/iX Server connections. Please see the chapter "Programming for PAD, DTC Telnet, Telnet/iX Server and VT Devices" in this manual for more details.

A DTC with a Telnet Access Card (TAC) provides Telnet access to an MPE/iX system. Only one TAC is needed per network. The terminal data is transmitted to the Telnet Access Card in the DTC. The DTC then transmits the data to the MPE/iX system. For the purposes of asynchronous serial communications, the terminals connected through DTC Telnet are non-nailed devices with special control restrictions. Those restrictions are noted in this manual where appropriate. Otherwise, DTC Telnet is transparent to your program.