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Terminal Controlled Keys
The device may provide typematic operation for some or all keys on the keyboard;
see the device manual for details. (When a typematic key is pressed, its function is
repeated as long as the key remains pressed.) Also, keys such as SHIFT and LOCK
may exist on the device. Refer to the device documentation for a description of how
the device supports them. These types of keys are not detected by the 3708 and are
controlled entirely by the device.
Keys vs. Key Sequences
At an actual 3270 terminal, the keyboard functions are nearly always associated with
one key on the keyboard. For example, the PFI function is achieved by pressing the
key labelled "PFI". However, the ASCII terminals that are supported by the 3708
generally do not provide keys labelled to match all the possible 3270 functions.
Therefore, the user must sometimes press two keys to cause one function. (For
example, ESC I causes the PFI function on many of the supported terminals.)
Every time the user presses a key (or in some cases "Alt" or "Ctrl" plus another key)
on the terminal, a hexadecimal (ASCII) code is transmitted to the 3708. These codes
are used to identify the function the user wants to do. The 3708 does whatever is
necessary to perform the function: it may send other hexadecimal codes back to the
device that cause the cursor to be repositioned; it may initiate the transmission of
data to the host; or it may echo back a data character for display on the screen.
The keyboard map defined for the terminal type describes what keyboard function
the 3708 associates with the key sequences pressed on the keyboard. For more
description of the keyboard map, see "The Terminal Table Format" on page 4-54.
To avoid confusion, this document refers to 3270 and non-3270 "functions" to
identify keyboard activity that would be represented by one key on a real 3270
device. To perform one of these functions, a "key sequence" from the ASCII
terminal is used. The keyboard map for the device tells the user exactly what key or
keys on the keyboard to press to cause the desired function.
Key Sequences for 3270 Functions
The following descriptions of keyboard functions are applicable to all terminals
supported by the 3708, except where noted. In some cases, these descriptions
contain SNA protocol terms, references to local copy operations, or status line
information.
Cursor Movement Function (Cursor Up, Cursor Down, Cursor Right, and Cursor
Left):
This set of four functions moves the cursor one position at a time into any
character location. Using these functions, the cursor may be moved into any
location, including unprotected and protected fields.
The following functions are all capable of causing the cursor to wrap:
• If the cursor is located in the last position of a line and you use the cursor right
function, the cursor is positioned in the first position of the next line.
• If the cursor is located in the first position of a line and you use the cursor left
function, the cursor is positioned in the last position of the previous line.
• If the cursor is located in the first line of the screen and you use the cursor up
function, the cursor is positioned in the last line of the screen, without changing
the column position.
• If the cursor is located in the last line of the screen and you use the cursor down
function, the cursor is positioned in the first line of the screen, without changing
the column position.
4-46
IBM 3708 Description
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