AM3270/TR3271 Reference Manual

Level 4 Protocols
Overview of AM3270 and TR3271
086705 Tandem Computers Incorporated 2–3
CRT display mode (CRT) protocol
Printer mode (PRT) protocol
Quotron (QUO) protocol
AM3270 and TR3271 subdevice protocols are specified through SCF, not SYSGEN;
therefore, command interpreters accessing 3270 terminals may be brought up only
after executing SCF commands.
Note The Communications Management Interface (CMI) can also be used for C-series releases, but it has less
functionality than SCF, and Tandem recommends that you use SCF. Support for the CMI interface and
the 6202 controller for AM3270 and TR3271 are discontinued for D-series releases.
For more detailed information about these protocols, refer to the discussions of
subdevice protocols in Sections 4 and 6.
ITI Protocol The ITI protocol provides an interactive terminal interface for an individual terminal.
An example of this use is to allow access of a Tandem command interpreter from a
3270 terminal).
AM3270 provides a minimum level of screen control for a terminal configured in ITI
protocol. The interface is one line at a time. AM3270 maintains a line count.
Successive WRITES to the screen are placed on a new line.
When the line count indicates that the screen is full, AM3270 reads the screen and
awaits operator input before continuing. When the operator presses the ENTER key,
the screen is cleared and the next group of lines is displayed.
A READ request causes the the next line to be unprotected; the cursor is positioned at
the start of the line and the terminal is ready for input. The WRITE following a
WRITEREAD operation causes the screen to be cleared and the cursor to be positioned
on the next line following the written data.
PTP Protocol The PTP protocol implements the “pass-through” function, which provides the ability
to interconnect an AM3270 subdevice directly to a TR3271-designated subdevice
without an intervening application process. In this mode, a complete communication
buffer received from an AM3270 subdevice is automatically sent to the corresponding
TR3271 subdevice for forwarding to an IBM host. (Note that the “corresponding
TR3271 subdevice” is not a physical device, but a software designation recognized as a
subdevice by the system.)
When the terminal transmits blocks of data (each terminated in an ETB), the blocks are
accumulated into a single message by AM3270, which is then transmitted to the host
by way of TR3271. Polling is not restarted on the transmitting terminal until TR3271
acknowledges receipt of the complete message. Data received by TR3271 from the
host is sent to the corresponding subdevice in AM3270 and then transmitted to the
terminal device.
The AM3270 and TR3271 processes that are communicating to provide the pass-
through function may be in different Tandem systems and connected anywhere in an
Expand network.