Commands and options for terminals and logical units

Fullword lengths

Option           Alternative
 
LENGTH           FLENGTH
TOLENGTH         TOFLENGTH
FROMLENGTH       FROMFLENGTH
MAXLENGTH        MAXFLENGTH

Application programs must be consistent in their use of fullword and halfword options on terminal control commands. The maximum value that can be specified as a parameter on any length keyword is 32 767.

Read from terminal or logical unit (RECEIVE)

The RECEIVE command is used to read data from a terminal or logical unit. The INTO option is used to specify the area into which the data is to be placed. Alternatively, a pointer reference can be specified in the SET option. CICS® acquires an area large enough to hold the data and sets the pointer reference to the address of that data.

The contents of this area are available to the task until the next terminal I/O command. However, the area does not belong to the task and is released by CICS while processing the next request. Therefore, this area cannot be passed back to CICS for further processing.

The application can use MAXLENGTH to specify the maximum length of data that the program accepts. If the MAXLENGTH option is omitted on a RECEIVE command for which the INTO option is specified, the maximum length of data the program accepts can be specified in the LENGTH option. If the MAXLENGTH option is omitted on a RECEIVE command for which the SET option is specified, CICS acquires enough storage to hold all the available data.

If the data exceeds the specified maximum length and the NOTRUNCATE option is specified, the remaining data is made available to satisfy subsequent RECEIVE commands. If NOTRUNCATE is not specified, the data is truncated and the LENGERR condition occurs. In this event, if the LENGTH option is specified, the named data area is set to the actual data length (before truncation occurs) when data has been received. The first RECEIVE command in a task started by a terminal does not issue a terminal control read but copies the input buffer, even if the data length is zero. A second RECEIVE command must be issued to cause a terminal control read.

When a PA key is defined as a print key by the system initialization parameter PRINT, and that key is pressed in response to a RECEIVE command, it has no effect on the application program. The RECEIVE command is satisfied, and the application allowed to continue, when another attention (that is, one of the other PA keys, any of the PF keys, the ENTER key, or the light pen) is made at the keyboard.

Write to terminal or logical unit (SEND)

The SEND command is used to write data to a terminal or logical unit. The options FROM and LENGTH specify the data area from which the data is to be taken and the length (in bytes) of the data. For a transaction started by automatic transaction initiation (ATI), a SEND command should always precede the first RECEIVE in a transaction.

Unless the WAIT option of the SEND command is specified also, the transmission of the data associated with the SEND command is deferred until a later event, such as a sync point, occurs. This deferred transmission reduces the flows of data by allowing data flow controls to be transmitted with the data.

Transmission is not deferred for distributed transaction processing when interregion communication (IRC) is in use.

Synchronize terminal I/O for a transaction (WAIT TERMINAL)

This command is used to ensure that a terminal operation has completed before further processing occurs in a task under which more than one terminal or logical unit operation is performed. Alternatively, the WAIT option can be specified in a SEND command. (A wait is always carried out for a RECEIVE command.) Either method may cause execution of a task to be suspended. If suspension is necessary, control is returned to CICS. Execution of the task is resumed when the operation is completed.

Even if the WAIT option is not specified in a SEND command, the EXEC interface program ensures that the operation is completed before issuing a subsequent RECEIVE or SEND command.

Converse with terminal or logical unit (CONVERSE)

For most terminals or logical unit types, a conversational mode of communication can be used. The CONVERSE command is used for this purpose and means that the 3650 application program communicates with the host processor. If this option is not specified, the 3650 application program cannot communicate with the host processor. In general, the CONVERSE command can be considered as a combination of a SEND command followed immediately by a WAIT TERMINAL command and then by a RECEIVE command. However, not all options of the SEND and RECEIVE commands are valid for the CONVERSE command; specific rules are given in the syntax descriptions for different devices. The TOLENGTH option is equivalent to the LENGTH option of the RECEIVE command, and the FROMLENGTH option is equivalent to the LENGTH option of the SEND command.

Send an asynchronous interrupt (ISSUE SIGNAL)

This command is used, in a transaction in receive mode, to signal to the sending transaction that a mode change is needed. The execution of the command raises the SIGNAL condition on the next SEND or RECEIVE command executed in the sending transaction, and a previously executed HANDLE CONDITION command for this condition can be used either to action the request or to ignore it.

Disconnect a switched line (ISSUE DISCONNECT)

This command is used to break a line connection between a terminal and the processor, or to break a session between SNA logical units (LUs), when the transaction is completed. If the terminal is a buffered device, the data in the buffers is lost.

When used with an SNA LU, ISSUE DISCONNECT, which does not become effective until the task completes, signs off the terminal, frees the COMMAREA, clears the next TRANID, stops any BMS paging, and, if autoinstall is in effect, deletes the terminal definition.