You can specify in the DD statement, the DCB macro, or the data set label that an optional control character is part of each record in the data set. The 1 byte character is used to show a carriage control function when the data set is printed or a stacker bin when the data set is punched. Although the character is a part of the record in storage, it is never printed or punched. Note that buffer areas must be large enough to accommodate the character.

If the immediate destination of the data set is a device, such as a disk or tape, which does not recognize the control character, the system assumes that the control character is the first byte of the data portion of the record. If the destination of the data set is a printer or punch and you have not indicated the presence of a control character, the system regards the control character as the first byte of data. If the destination of the data set is SYSOUT, the effect of the control characters is determined at the ultimate destination of the data set. See z/OS DFSMS Macro Instructions for Data Sets for a list of the control characters.

The presence of a control character is indicated by M or A in the RECFM field of the data control block. M denotes machine code; A denotes American National Standards Institute (ANSI) code. If either M or A is specified, the character must be present in every record; the printer space (PRTSP) or stacker select (STACK) field of the DCB is ignored.

The optional control character must be in the first byte of format-F and format-U records, and in the fifth byte of format-V records and format-D records where BUFOFF=L. If the immediate destination of the data set is a sequential DASD data set or an IBM standard or ISO/ANSI standard labelled tape, OPEN records the presence and type of control characters in the data set label. This is so that a program that copies the data set to a print, punch, or SYSOUT data set can propagate RECFM and therefore control the type of control character.