AM3270/TR3271 Reference Manual

AM3270Specific FileSystem Operations and Procedures
A Closer Look at AM3270
086705 Tandem Computers Incorporated 3–5
Select/Write Operation When an application process calls the WRITE procedure, AM3270 will select the
appropriate terminal or printer. Outbound text contains the appropriate
communication characters (STX,ESC,ETX), which are inserted prior to the
transmission of text to the subdevice.
Each message is written to a device as one WRITE operation. When the message has
been transferred, AM3270 sends an EOT that completes the physical WRITE operation
and the write to the application process.
Figure 3-4 illustrates the select operation.
Figure 3-4 Select Operation
009
AM3270 sends an EOT
Request for the subdevice is completed
Subdevice acknowledges the message
Text is written to the subdevice
AM3270 selects the subdevice
AM3270 inserts STX, ESC and
ETX into message to be written
CALL WRITE
Subdevice acknowledges the selection