AM3270/TR3271 Reference Manual

TR3271-Specific Operations
A Closer Look at TR3271
5–6 086705 Tandem Computers Incorporated
Depending on the value for the SYSGEN INITSTATUS modifier, TR3271 must respond
to the host; otherwise, the host will no longer use the emulated terminal. In this
situation, TR3271 listens for polls and selects that are meant for the emulated device.
Any poll that is received causes an EOT to be returned by TR3271 to the host. The
EOT indicates that the device has no data to send.
Appropriate Select Responses
If the host selects an emulated terminal already added by SCF (but before an
application OPEN or SCF CONNECT is issued), TR3271 response depends upon the
setting of the system generation macro modifier, INITSTATUS. Values for
INITSTATUS are described as follows:
INITSTATUS = 0 (the default setting)
For this value (0), TR3271 responds to selects by returning a WACK to the host.
The WACK indicates that TR3271 is busy. The busy condition will exist until
either the application program issues an OPEN request to the addressed subdevice
or an SCF CONNECT command is issued. In this situation, a possible problem is
that the host front end might continue to send selects in response to the WACKs.
INITSTATUS = %177776
TR3271 will not respond to selects if this value is set at system generation. As a
result, the host will time-out the subdevice (if the addressed subdevice has not
been OPENed or CONNECTed).
INITSTATUS = %177777
This value causes TR3271 to respond to selects with an ACK0 and then continue
by acknowledging the data sent by the host. Because the data was not requested,
it is discarded. An appropriate message is logged to the operator console. The
message contains the TR3271 line handler’s logical device number (LDEV) and the
affected device’s subdevice number.
This value for INITSTATUS is useful only if nonessential data, such as unsolicited
informational messages, can be sent to the device before it is either opened or
connected.
INITSTATUS = any 16-bit value other than 0, %177776, or %177777
These remaining possible values are used by TR3271 as IBM status/sense bytes.
Using INITSTATUS in this manner causes TR3271 to respond to a select with an
RVI which signifies a status/sense condition. Any subsequent poll by the host
will result in the transfer of the status/sense bytes from TR3271 to the host. You
must ensure that status/sense information is in the correct format for the host.
For a more detailed discussion of sense and status bytes (which are displayed by
using the SCF command STATUS SU), including a table listing sense/status bytes,
refer to the SCF Reference Manual for AM3270 and TR3271.