Using sequential terminal support

One of the many types of terminal that CICS® supports is not really a terminal at all, but a pair of sequential devices or files simulating a terminal.

One of the pair represents the input side of the terminal, and might be a card reader, a spool file or a SAM file on tape or DASD. The other represents the output, and might be a printer, a punch, spool, or SAM file. Many device-type combinations are allowed, and either of the pair can be missing; that is, you can have an input-only or output-only sequential terminal.

You read from and write to the devices or files that constitute a sequential terminal with terminal control commands, specifically RECEIVE, SEND, and CONVERSE. (BMS supports sequential terminals too; see Special options for non-3270 terminals .)

The original purpose of sequential terminal support was to permit application developers to test online code before they had access to real terminals. This requirement rarely occurs any more, but sequential terminals are still useful for:

Printing: See Programming for non-CICS printers . Sequential terminals are useful for output that is sometimes directed to a low-speed CICS printer, for which BMS or terminal control commands are required, and sometimes directed to a high-speed system printer (spool or transient data commands). If you define the high-speed printer as a sequential terminal, you can use terminal control or BMS commands, and you can use the same code for both types of printers. (If there are differences in the device data streams, you need to use BMS for complete transparency.)
Regression testing: Tests run from sequential terminals leave a permanent record of both input and output. This encourages systematic and verifiable initial testing. Also, it allows you to repeat tests after modifications, to ensure that a given set of inputs produces the same set of outputs after the change as before.
Initialization: Some installations use a sequential terminal to execute one or more initialization transactions, in preference to program list table programs. Transactions initiated from a sequential terminal begin execution as soon as the terminal is in service, and they continue as quickly as CICS can process them until the input is exhausted. Hence the inputs from a sequential terminal can be processed immediately after startup, if the sequential terminal is initially in service, at some later time (when it is put in service) or even as part of a controlled shutdown.