Exchange/SNA Manual

OPEN Procedure
Exchange/SNA System Procedure Calls
104700 Tandem Computers Incorporated 5–15
Considerations The OPEN procedure establishes communication between your program and a
subdevice supported by the Exchange/SNA line server. The above description of the
OPEN procedure describes the minimum requirements for establishing
communication with an Exchange/SNA subdevice. This description omits a number
of parameters that might be useful in your particular situation. For a complete
description of the OPEN procedure and its parameters, see the Guardian Procedure Calls
Reference Manual.
Before you can call the OPEN procedure, the specified line server must have been
started, and the configuration of that line server must support the specified subdevice.
You specify the configuration of a line server using the SET command. You start the
line server with the CONNECT command. See the SET command and the CONNECT
command in Section 3 for more information.
You must call OPEN before you can perform any I/O operations using the specified
subdevice. All I/O operations must identify the subdevice by the file number
returned by OPEN.
The Exchange/SNA line server allows each subdevice other than the console
subdevice to be opened by only one process (and the backup process, if one exists) at a
time. This restriction is enforced by the line server regardless of the exclusion mode
you specify in flags . The number of processes that can open the console subdevice at
once is specified in the CONSOLE parameter of the SET command (or the RJECIS
command). See the SET command in Section 3 for more information.