Host Control Program Communication; Light Pen Simulation; Selection Fields - IBM 3174 Reference Manual

Using Your ASCII Terminal
Action: Use the DEV CNCL key sequence to clear the keyboard-locked
condition. Try your print request again after starting the printer, or use
IDENT to change your print ID and request a different printer.
Host Control Program Communication
After you begin an application session, you can communicate with the host control
program by using the SYS REQ function. When you use the SYS REQ key
sequence, your screen is cleared.
When you send messages to the control program, you can only type a message
beginning at the current cursor location. The message can be up to 256 characters
long. When you press Enter, the data, beginning with the original cursor location
and extending 256 positions or to the end of the screen, is transmitted to the host.
Data received from the control program is displayed at the current cursor location.
When you are using the SYS REQ function, the following functions are not
available:
• PF1-PF24
• PA1-PA3
• ATTN.
If you use one of these key sequences, the keyboard is locked and the invalid
function status line message (X -f) is displayed. You can unlock the keyboard by
using the Reset key sequence defined for your terminai and repositioning the
cursor.
You can return to your application program session by entering the SYS REQ key
sequence again.
A common use of this function is to log off the active application. You can use the
SYS REG key sequence to start communication with the host control program, then
type a logoff request as defined for your installation.
Light Pen Simulation
A selector light pen is a light-sensitive pen that can detect the light emitted from
characters displayed on certain 3270 terminals. With the pen, you can select from
a list or table of displayed items and then cause those selections to be passed to
the application program. The 3174 allows you to simulate this light pen function
using the Cursor Select function. This simulation is done by positioning the cursor
(using normal cursor movement functions) in the field that you wish to select, and
then entering the Cursor Select key sequence. Depending on the way that the host
program defines the field, you obtain various responses. See the keyboard maps
in Appendix A, "Keyboard Maps for ASCII Terminals Used as 3270 Terminals" on
page A-40 for the Cursor Select key sequence.
Selection Fields
A selection field is identified by a question mark (?) in the first position of a field.
To select the field, place the cursor anywhere in the field that you want to select,
and then use the Cursor Select key sequence. The question mark is changed to a
greater than (>) symbol. To reverse your selection, use the Cursor Select key
sequence again. The greater than (>) symbol is replaced by a question mark (?).
Chapters. Using Your ASCII Terminal 3-19