McKown, John wrote:
> You mean you want more than two different screen sizes? That is not
particularily a TSO restriction, it is a 3270 data stream restriction. A
3270 can only have two different screen sized, based on the 3270
architecture. There is the "normal" size (usually, but not necessarily
24x80) which is "switched to" with the ERASE/WRITE command. There is the
"alternate" size (whatever is specified in the emulator/VTAM BIND image)
which is "switched to" with the ERASE/WRITE ALTERNATE command.
Does a 3180 qualify as a 3270? It supports dynamic switching among four
screen sizes (provided the hardware is so set up). A program may switch
to one of these, or may use any screen configuration that fits in the
buffer (done by specifying the size of an explicit partition). I got
quite a surprise when I defined a screen of 24*80 and on the first try
had the values reversed - got 80 lines of 24 bytes.
I have (non-TSO) programs that allow the user to switch on the fly
(though not in the middle of a command), and doing so doesn't even
require fiddling with VTAM definitions.
In order to have "n" different screen sizes would be a horrendous
challange to TSO and VTAM as well. First, IBM would need to implement a
new "write" command (WRITE/ERASE SELECT SIZE or something like that).
But then they'd need to update the defination of LU type 2 in VTAM to
handle "n" possible screen sizes. Now TSO must keep track of the various
possible screen sizes and select the "most appropriate" one. Oh, the
TN3270E defination and emulators would need to be updated to support
this as well. And always remember that the 3270 data stream does __NOT__
tell how to position the current write location using x,y coordinates.
It uses "buffer addresses" which are basically "number of bytes from the
beginning of the screen image". The TN3270E emulator converts whese to
actual x,y positions on the screen.
No special command is needed, only the use of explicit partition size
definition. TSO can continue to use the default size from the BIND
negotiation, and let the user switch later. VTAM functions correctly
with the "generic" 3270 settings. Some emulators already support
on-the-fly screen switching (e.g., BlueZone, which I mentioned in
another post).
The x,y problem is solved by restricting the row and column sizes to a
maximum value of 255, and coding the x,y position directly. The
appropriate output routine can scan through the buffer and build the
correct coordinates.
This would be very expensive for a "dying" technology. If it were me,
I'd be looking at something to totally replace TSO.
At least we agree - it would not be cost effective.
Gerhard Postpischil
Bradford, VT
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