SNA character string controls

SNA character string controls (SCS) describe specific functions for the EBCDIC control codes. You can use the primary functions that are described to format a printed page or an alphanumeric display screen.

Functions are also defined for codes that set modes of device operation, define data to be used in a unique fashion, or are used for communication between a device operator and an application program (where the specific function associated with the code is defined in a protocol established between a program and an operator).

An SCS data stream consists of a sequential string of control and data characters. Control function characters in the form of SCS-defined control codes can be intermixed with graphic data characters. Other data types (such as binary and packed decimal) are permitted only in conjunction with the transparent (TRN) control.

SCS control codes appear within the data portion of the request unit (RU). A function management (FM) header can precede SCS data within an RU. Functions such as component selection are performed by FM header functions and are not included as SCS functions.

SCS functions do not include data flow control functions, even when these functions are available to a keyboard operator through keys on the keyboard. For example, CANCEL is a data flow control request that can be initiated by a key on the keyboard.