AM3270/TR3271 Reference Manual
AM3270Specific FileSystem Operations and Procedures
A Closer Look at AM3270
3–4 086705 Tandem Computers Incorporated
Figure 3-3 illustrates the poll operation.
Figure 3-3. Poll Operation
AM3270 adds the
subdevice to the poll list.
008
CALL OPEN
?
?
?
Communication Line
is Polled
Text Block Received
CALL READ
Acknowledge the message and
complete the READ request.
Did a polled station respond with text?
Does the station have a READ pending?
Is the last character an ETX?
no
no
no
yes
yes
yes
NAK Block to Wait for READ
Acknowledges the message
and reads the next block from
the subdevice.
no
Message text sent to, or received from, a subdevice is filtered by AM3270. Inbound
text received from the subdevice is collected in blocks. Communication and control
characters (STX,ETX,ETB) are stripped from the data by AM3270. When all of the text
has been received from the subdevice, the complete buffer and the actual text byte
count are returned to the application.
If a device responds to a general poll and there is no READ request pending, the data
will be rejected (NAKed n number of times, where n is the retry count) and finally, an
EOT or an RVI will be sent (depending upon which system generation parameter was
specified, EOTIFNOREAD or RVIIFNOREAD). For AM3270 and TR3271 the retry
count is incrementally one greater than (not equal to) the last retry count.