AM3270/TR3271 Reference Manual

Details of the ITI Protocol
AM3270 Subdevice Protocols
4–6 086705 Tandem Computers Incorporated
cpu,pin = enable BREAK.
buf[1] terminal access mode after BREAK is typed.
0 normal mode (any file type access is permitted).
1 BREAK mode (only BREAK-type file access is permitted).
Where buf[2] and buf[3] are the two words of the 32-bit tag. This tag is saved by
the I/O process handling the 3270 terminal.
Whenever AM3270 detects the input of a PA1 key (simulated BREAK) from a 3270
terminal configured for ITI protocol, a BREAK message LCB is sent to the owner of the
BREAK for that terminal. (The BREAK owner is specified by the parameter in buf[0].)
The six parameter words of the BREAK message are:
P1 a -20 (identifies this as a BREAK message).
P2 logical device number of the I/O process.
P3 system number of the I/O process.
P4 most significant word of the BREAK tag.
P5 least significant word of the BREAK tag.
P6 a 0 (zero).
To file-system users, the BREAK message LCB parameters P1 through P6 appear in a
buffer read from $RECEIVE as buffer[0] through buffer[5]. The BREAK tag is
checkpointed by the I/O process to its backup (to satisfy Guardian 90 requirements).
WRITE Request A WRITE request causes polling to be halted. A select operation is initiated for the
subdevice. If the select is accepted with no error received from the device, AM3270
adds the communication characters to the text to be written and writes it to the device.
Successful completion of the WRITE by the device causes the WRITE to be completed
to the application process.
A WRITE advances an internal line counter by one. If the new line count positions the
next line to be written at the bottom of the screen, the subdevice is put on the poll list
(in effect, the subdevice is waiting for some keyboard input before proceeding with
further output).
Output that is started after the keyboard input is accepted causes the screen to be
cleared and the first line of output to be displayed at the top of the screen. A WRITE
following the READ completion of a WRITEREAD request also clears the screen and
positions the next output at the top of the screen.
WRITEREAD Request A WRITEREAD request is processed by AM3270 as though a WRITE request followed
by a READ request was received from the application process.
Error Handling Errors returned by AM3270 are the result of receiving either no response or an
improper response from the physical device. If notified of the presence of status
information from the device, status is solicited by AM3270 using a specific poll. In this
case, errors returned to the application process result from a translation performed by
AM3270 based on the actual status received by the device.