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Terminal Tables
The following section describes how terminal tables are used to control displays.
It
also describes the two types of terminal tables supported by the 3708.
Controlling Displays With Terminal Tables
When performing protocol conversion to a display, the 3708 must interpret the host
data stream and convert it into control commands and data that the display
Uliderstands. The 3708 must send ASCII sequences to the display to cause, for
example, the terminal to clear its screen. However, the sequence required to cause
the function may be different for each terminal type. For this reason, the 3708 uses
a terminal table to control each type of terminal.
The terminal table also describes the keyboard map for the terminal. When a key
(or in some cases "Alt" or "Ctrl" plus another key) is pressed at a terminal, a
hexadecimal (ASCII) code is transmitted to the 3708. These codes are used to
identify the desired function. Because the codes generated by one terminal type for a
certain key (for example, PFI) may be different than the codes generated by another
type, the terminal table must be used to define to the 3708 what to expect from the
device.
The tables for the default terminals are part of the microcode contained in the 3708
cartridge; however, user-defined tables may be added as part of the configuration.
These tables allow you to define a unique keyboard mapping for a supported
terminal or define an entirely new terminal type. A user-defined table (UDT) is
saved in the nonvolatile storage of the 3708 base unit.
Standard and Enhanced Terminal Tables
The 3708 has two sizes of terminal tables: standard and enhanced. Standard tables
are 300 bytes long, and enhanced tables are 452 bytes long. Enhanced tables must
be used for 3270 model 3, 4, and 5 emulation (large screens). Enhanced UDTs can
be used to customize the UDT names that are displayed on the terminal selection
screen (C2) when a user logs on to the 3708. Enhanced UDTs can also be used to
customize the terminal initialization sequence that is sent to the terminal at the start
of each protocol conversion session.
There are five restrictions in the use of enhanced UDTs:
1. You can define only four enhanced UDTs. You can use six standard UDTs.
2. You cannot mix standard and enhanced UDTs.
3. Before defining an enhanced UDT, you must convert the standard UDTs to
enhanced UDTs. Refer to IBM 3708 Network Conversion Unit Planning and
Installation for instructions.
4. You can also convert enhanced UDTs to standard UDTs. However, you lose
the ability to have user-defined UDT names and user-defined initialization
sequences, and you are not able to operate in large-screen mode using the
UDTs. Refer to IBM 3708 Network Conversion Unit Planning and Installation
for instructions.
5. If you have enhanced UDTs and you need to convert to a microcode level prior
to A58809, you must first convert enhanced UDTs to standard UDTs.
Chapter 4. Protocol Conversion Mode
4-53
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