STCC - Specify Terminal Control Characters

Use the STCC macro instruction to specify what control characters will be used to delete a character or a line of terminal input.

When the line-delete control character specified in the STCC macro instruction is encountered within a line of terminal input, the line control character and all the preceding characters in that line are deleted. When the character-delete control character specified in the STCC macro instruction is encountered within a line of terminal input, the character-delete control character and the character immediately preceding it are deleted from the line.

When the user is logging on, he can delete a line or character by using the system-supplied defaults. The defaults, according to the type of terminal, are as follows:

Type of terminal	Desired action	Key(s) to be pressed
1050 and 2741	Line deletion or character deletion	Attention key and backspace
33/35 Teletype	Line deletion or character deletion	CTRL and X key (X'18.'), back arrow (<-), or underscore (_), depending on keyboard. (Either key results in X'6D'.)
3767/3770	Line deletion or character deletion	Attention key and backspace

No defaults are defined for the display stations, because the terminal user can use cursor control keys more effectively to delete characters or lines before the input is transmitted to the system.

The STCC macro instruction is valid in a time sharing environment with terminals (other than LU_T1 devices) that use TSO/E with the exception that ATTN/NATN is not supported in a VTAM® environment. STCC is ignored if TSO/E is not active when the macro instruction is issued.

Figure 1 shows the format of the STCC macro instruction; each of the operands is explained following the figure.

Figure 1. The STCC macro instruction

  [symbol]     STCC       [ATTN] [,LD={X'n'}+
]  [CD={X'n'}]
                          [NATN] [    {C'c'}+
]  [   {C'c }]

ATTN | NATN

ATTN: When this operand is in effect, pressing the ATTENTION key after having typed data will only delete the current line. System response is !D. Automatic prompting is not turned off. The ATTENTION key can then be pressed again, without typing any input, to interrupt the program and turn off prompting. When this operand is not in effect, the attention key will both delete a line of terminal input and interrupt the execution of the user's program. System response is ! or !I.
NATN: indicates that the attention key will not be used to delete a line of terminal input.

LD=

indicates what character will be used for the line delete control character:

X'n': where X'n' is the hexadecimal representation of any EBCDIC character on the terminal keyboard, except the new line (NL) and carrier return (CR) control characters. If X'00' is specified, the previously used line-delete control character is retained. If X'FF' is specified, no character will be used for the line-delete control character. If an incorrect character is specified, that character is rejected and no character is used to delete a line of terminal input.
C‘c’: where c is the character representation of any EBCDIC character on the terminal keyboard.

CD=

indicates what character will be used for the character-delete control character:

X'n': where X'n' is the hexadecimal representation of any EBCDIC character on the terminal keyboard except the new line (NL) and carrier return (CR) control characters. If X'00' is specified, the previously used character-delete control character is retained. If X'FF' is specified, no character will be used for the character- delete control character. If an incorrect character is specified, that character is rejected and no character is used to delete a character from a line of terminal input.
C‘c’: where c is the character representation of any EBCDIC character on the terminal keyboard.

When control is returned to the user, the low-order byte of register 0 contains the former line-delete control character. If X'FF' appears in the low-order byte of register 0, there is no former line-delete control character. If X'80' appears in the high-order byte of register 0, ATTN was in effect for line deletion prior to the issuance of the STCC macro.

The low-order byte of register 1 contains the former character-delete control character. If X'FF' appears in the low-order byte of register 1, there is no former character-delete control character.

Table 1. Return codes from STCC
Return code dec(Hex)	Meaning
0(0)	Successful.
4(4)	Incorrect parameters were specified to the SVC.
8(8)	The request is not valid because either the specified character does not appear on the terminal keyboard, or ATTN was specified for a terminal that does not have an attention key.
12(C)	The terminal type is not valid.