AM3270/TR3271 Reference Manual

Details of the CRT Protocol
AM3270 Subdevice Protocols
086705 Tandem Computers Incorporated 4–9
Loss of Communication If communication between line handlers in separate systems on a network is lost, no
special action is taken.
If the failure was due strictly to communication loss, the two line handlers continue
when communication is restored. If the failure was due to a system failure/reload, the
SCF CONNECT command can be performed again, using the reloaded system as the
local system.
The remote end accepts CONNECT requests from a line handler/subdevice to which it
is already connected if no parameter (with the exception of NAME) changes.
Error Handling Because a pass-through subdevice has no application process initiating requests, errors
must be handled by the pass-through protocol itself. Normally an application process
would determine what to do if an error was returned; for example, the application
could discontinue operations to a device that was operating erratically.
For PTP, if a request is initiated and completes without error, an error counter is
cleared. If the request results in an error reported to the subdevice and the error count
is greater than 3, the subdevice will be disabled and must be manually brought back
up with SCF. Disabled subdevices are reported to the local system operator console.
Details of the CRT
Protocol
AM3270 subdevices assigned to the CRT protocol expect data buffers passed from an
application to contain standard 3270 buffer orders and text.
AM3270 does not look at the contents of the data buffer. Communication-related
characters such as STX, ETB, and ETX, are added or stripped depending upon whether
the data is inbound or outbound.