Exchange/SNA Manual

Step-by-Step Instructions
Using the Exchange/SNA Programmatic Interface
104700 Tandem Computers Incorporated 4–11
Each subdevice, other than the console subdevice, must be opened for exclusive access.
The console subdevice can be opened for shared access. The following table shows the
type of access for which you should open each type of subdevice.
Subdevice Access
Console Read/Write or read-only (not write-only)
Printer or punch Read-only (you receive files from these devices)
Card-reader Write-only (you send files to these devices)
The type of operation you want to perform determines the subdevice class you need to
open. If you want to send commands to the host RJE subsystem, you must open the
console subdevice. If you want to send data to the host system, you must open a card-
reader subdevice. If you want to receive data from the host system, you must open a
printer or punch subdevice. Moreover, the particular subdevice you open must match
the destination subdevice selection specified by the host system for the data stream
you want to receive.
Step 3: Set the Operational
Parameters
Before your program sends data to or receives data from the host system, your
program can set the parameters that control the send or receive operation. (This
information does not apply to console operations.) Call the SETMODE procedure to
set the parameters. Call SETMODE with function equal to 42 to specify the
parameters for a send operation (calls to WRITE); call SETMODE with function
equal to 43 to specify the parameters for a receive operation (calls to READ). For
information on the parameters and how to specify them, see the SETMODE procedure
as described in Section 5.
If your program does not call SETMODE to set the parameters for a send operation or
a receive operation, the line server uses the default values for the parameters. See the
SETMODE procedure in Section 5 for the default values.
The operational parameters are set separately for each individual subdevice supported
by the line server. Your program can set the parameters one way for one subdevice
and another way for another subdevice and then perform concurrent operations on the
two subdevices. In general, unless you want to use the default values for the
operational parameters, your program will call SETMODE at least once for each
separate subdevice used by your program.