Re: Trying to display subfile

[dhandy@xxxxxxxxxxx (Douglas Handy)]

Colin, et al:

>I don't know. Does anybody on the list?
>
>> So does that rule apply in 5250 emulation?
>> 
>> The original 5250 hardware had a limit of 128 fields.
>> I don't think that has changed.

It depends on what your devices are hooked up to.  The limit isn't in
the device; it is in the WS controller.  Even a vintage 5251-11 hooked
up to today's AS/400 twinax controllers can handle more fields than
when connected to the original controller design.

The oldest 5250 Functions Reference Manual that I still have is the
thrid edtion from May 1980.  But my older S/34 Functions Reference
Manual actually has a much better description of how to compute the
maximum for a given display format.  

The limitation is due to the workstation controller's size for what is
called the "format table".  This is where the controller stores
information on each input field on the active format.

The original 5250 WS controllers (e.g., the S/34 or 5251 remote
controller) had a format table of 512 bytes per workstation.  Each
input field takes either 4, 6, 8, or 10 bytes depending on the
attributes of the field.  The best case scenario is (was) 127 input
fields at 4 bytes each because 2 bytes are needed to mark the end of
the format table.

Input fields always took a minimum of 4 bytes, plus 2 bytes each for:
 - Field resequencing (not in row/col order within the buffer)
 - Modulus 10 or 11 check digit verification
 - Magnetic Stripe Reader (MSR) or Selector Pen (SP) capable

In addition, if any of the fields allowed MSR, the format table
reserves room for storing the MSR data plus three bytes (up to 128
bytes maximum).

The WS controllers on the S/36 came in two flavors (excluding
Ideographic) depending on whether or not you ordered the "Extended
Input Fields" feature.  The standard WS controller had a format table
of 770 bytes while the extended input fields feature had a format
table of 1526 bytes.  In both cases 2 bytes were still needed to mark
the end of the format table, leaving either 768 or 1524 bytes for the
input field definitions.  But the S/36 also added one other 2-byte
word per field to what it sent to the format table, so it took
anywhere from 6-12 bytes per field instead of 4-10 like the S/34.  The
result is that the 770 byte standard controller also held a maximum of
128 fields compared to the 127 on the S/34.  With the extended input
fields feature, you could get up to 254 fields if you didn't use field
resequencing, mod 10/11, or MSR.  (The only S/36 Functions Reference
Manual that I have is the sixth edition, so this may not have been
true of the earliest 5360 models.)

I don't have a S/38 Functions Reference, and don't remember what its
input field limits were.  Maybe somebody else does.

I can't find definitive information on the AS/400, but the format
table appears to be slightly larger than the S/36 controller with
extended input fields, and uses a similar algorithm.  Each field takes
a minimum of 6 bytes in the format table which must be somewhere
around 1538 bytes (256 fields * 6 plus 2 byte trailer).

The Application Display Programming manual has you reduce the 256
field maximum for MSR or SP usage, but says nothing about the other
optional 2-byte Field Control Words like Mod 10/11 or field
resequencing.  The 5494 Functions Reference, however, makes it clear
that several other features of the enhanced WS controllers also add a
2-byte FCW to the format table for occurence of any of these:
 - Continued entry field
 - Word wrap field
 - Cursor progression entry field
 - Highlighted entry field
 - Forward edge trigger entry field
 - Transparency entry field

Since a field takes a minimum of 6 bytes in the table and each
optional FCW takes 2 bytes, I suspect you would need to reduce the 256
field limit by one for every three options listed above (including Mod
10/11, MSR/SP, or field resequencing).

Also, remember remote displays depend on the controller:
 - 5294 has a maximum of 128 fields
 - 5394 has a maximum of 256 fields
 - 5494 has a maximum of 256 fields but supports the enhanced FCWs

And then there is the question about whether any of this aplies to
5250 emulation.  AFAIK, it does when using twinax, because you are
still really using the host WS controller where the format table
resides.  (Which is why even old emulation cards or 5251-11's can
support the new features of the enhanced WS controllers.)

I am less sure what happens when connected via Ethernet or Token-Ring.
I don't know for sure who is really performing the WS controller
functionality in this case. (I gave up caring about hardware details
in my S/36 days.)   But in any case I doubt the limits are lower than
the AS/400 enhanced twinax controller.

Having said all that, I'm not convinced this is related to Colin's
problem.  He is getting MCH1210, not CPF5192 like you should if the
limit is exceeded.  He also thought there were only about 80 input
fields.  It would be hard to get the limit down to 80; every field
would need an average of 7 optional FCW's.

Aside to Colin: Input-capable fields which are protected are still in
the format table.  How did you count your 80 fields?

With a program name like QWsSflCt,you'd surmise it had something to do
with the subfile control format, although the program has no text
description on my system.  I'd do a formatted dump on the error, or
run under debug and take a look at the contents of all of the fields
on the control format, including hidden or program fields, to make
sure they are within range.

Just my .02,
Doug
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