AM3270/TR3271 Reference Manual

Details of the PTP Protocol
TR3271 Subdevice Protocols
6–8 086705 Tandem Computers Incorporated
block at a time. When the last block has been acknowledged by the host, TR3271
completes the WRITE request to the application process.
If the host issues a general poll, and status other than device busy is set, TR3271
returns a status message instead of message text. If the host issues a specific poll, and
any status is pending, TR3271 returns that status instead of text. In neither case is any
pending WRITE request completed. When the host receives a status message, it
ordinarily responds with either ACK or RVI. If it does, the status for the subdevice is
cleared; otherwise, the status is retained.
Error Handling TR3271 retries operations, whenever appropriate, within BSC and 3270 guidelines. If
an operation fails repetitively and exhausts the retry count, or cannot be retried,
TR3271 returns an error code completing the request. Table 6-1 lists some of the errors
that could occur for READ, CONTROL 22, or WRITE operations.
Table 6-1. READ, CONTROL 22, or WRITE Request Errors
Operation/Error
Number Description Action/Indication
READ 171 No response. The host has selected the
subdevice but has failed to send text in
response to the acknowledgement.
Probable communications
hardware problem or host is
down.
READ 173 Text sent by host resulted in NAK for the retry
count
Indicates a communications
hardware problem.
READ 177 Text Overrun. The incoming message was
larger than the record size set at system
generation for the line.
Increase the record size of the
line.
WRITE 171 No Response. The host issued a poll but did
not respond to the text sent by TR3271.
Same as READ 171.
WRITE 172 Improper Reply. The host responded to text
with an invalid control sequence.
Generally indicates a host
problem.
WRITE 173 Text sent to the host resulted in NAK by the
device for the retry count.
Most likely cause is invalid
characters appearing tin the
application buffer.
Details of the PTP
Protocol
The PTP protocol provides the ability to logically connect a TR3271 emulated
subdevice directly to an AM3270 subdevice without an intervening application
process. This capability is normally used to attach certain subdevices controlled by
AM3270 directly to a host system.
The SCF commands ADD and CONNECT are used to add subdevices. The
CONNECT message is sent to either of the line handlers; the receiving line handler
validates parameters pertinent to itself, such as the existence and availability of its
subdevice. It then sends a message to the other line handler which performs a similar
set of actions and completes the joining of the subdevices if all conditions are correct.