TCVIEW displays the contents of the TCAP portion of the ZCPR3
environment descriptor or of a file which contains the TCAP module.
There are 3 widely distributed versions of TCAP, each associated
with unique versions of VLIB. TCVIEW properly displays all three
versions and reports the VLIB versions for which they were intended.
Included in this library are three example TCAP files, TC1.Z3T, TC4.Z3T,
and TC4D.Z3T. You can use TCVIEW24 to examine the structure and content
of these 3 main versions of Tcap files if your environment includes a
terminal descriptor (any version TCAP).

The following discussion is a brief history of VLIB/TCAP development,
the close relation between the two, and the importance of having the
latest version (currently -4D) in your system.

A TCAP is a 128 byte block which contains the data bytes that must
be sent to a terminal to control its functions. A Z-System needs a
TCAP specific to the system console if such functions as cursor
positioning, highlighting, and screen editing are to be implemented
by a program written for portability from one computer to another
whose terminal may be different. Terminals from different manufacturers
may use different code bytes to control terminal functions. If the
appropriate TCAP is installed in the Z3 Environment, then a program
that needs to position the cursor can index into the TCAP for the
proper code sequence and send that to the terminal. This is possible 
because the TCAP is a well defined data structure.

The subroutines required to display highlighted text with cursor 
positioning using TCAP data can be written as part of the source code
for an application program (like the ZMATE text editor, for example).
Since such routines are tedious to write and they be required in
many programs, a complete set of routines has been collected into a
Rel library for inclusion when the program is assembled and linked.
That library is named VLIB. Almost all screen oriented Z-System utilities
make use of VLIB.

The initial versions of VLIB and the TCAP definition are described in
ZCPR3 THE MANUAL, by Richard Conn. Since their introduction, VLIB has
been revised several times to add functions or optimize routines and
sometimes to correct errors. The definition of the TCAP did not change.
The last major revision number was Version 3. This TCAP and the
corresponding VLIBs contained no provision for the use of character
graphics which are included in most modern terminals. Control of
character attributes like underlining was also not addressed but was
needed for programs like Wordstar 4.

VLIB version 4, along with an extended TCAP definition, provided access
to the Character Graphics set, and a few demonstration programs were
written and distributed along with TCAPs for a number of the more popular
terminals.

There was trouble, however. A method of optimization had been overlooked,
and control of character attributes had not been included. After several
unreleased revisions, VLIB version 4D was released along with a new TCAP
structure definition. This version has met with general acceptance and
appears to be stable.

Programs written to use only the facilities afforded by VLIB 1, 2, or 3
execute with no problems when one of the later TCAPs is present. Programs
assembled with VLIB 4 that use character graphics will not operate properly
with any other TCAP; the same is true for VLIB 4D and its TCAP. Since
all three versions of TCAPs have been written and released, it becomes
important to be able to examine and identify the version of TCAP files
whose ancestry is unknown. THAT is what this version of TCVIEW does.

Some users would like additional data to be included in the TCAP. If this
were to be done, several criteria should be met:
1) The new TCAP should be downward compatible with that for VLIB 4D so
   that existing application programs will continue to work.
2) New data should not cause the size of the TCAP to exceed 128 bytes.
3) A new version of VLIB would need to be generated. This is a major task!

		Al Hawley,  12 July 1990
		Ladera Z-Node (Z-Node #2, aka ZNODE Central)
		(213) 670-9465