9. Maintenance and Fault Finding
GEM80-400
Page 9-12
ALSPA GEM
80-400 SERIES CONTROLLERS TECHNICAL MANUAL
Issue 3 04/99
end of a table, a specific reference must be included to create a large enough
table.
2. Also note that existing data table locations will be removed if they are no
longer required by a program that has been modified. This can create confusion
in the case of the P-table since they may be created simply by attempting to
access them through a suitable GEM
80 programming tool, such as Gemesys 3.
Consider the situation where an address list containing P1000 has been created
and the value 21 written to it. The program (which contains no reference above
P500) is then re-compiled. On re-entering the data list mode, the message
INVALID ADDRESS is displayed. If the list is cleared and P1000 re-entered, it will be
found to contain 0 and not 21. This is because P1000 had been deleted on
recompilation, but then recreated when the data list was renewed.
(2)
Generating and checking the I/O configuration data for Basic and
Verification I/O.
(3)
Checking the legality of data table accesses, e.g. OUT to a P-table is
not allowed
(4)
Checks the structure of the user program, e.g. depth of nesting of
Obey Blocks.
(5)
Checking the correctness of VALUE instructions with COUNT and
DELAY GEM
80 Special Functions. This checking ensures that if a
VALUE is required, it is present and of an acceptable type (e.g.
write-enabled data table).
(6)
Checking that there is a START OF BLOCK instruction for every END OF
BLOCK instruction and vice versa, and checking LABEL and JUMP
GEM
80 Special Functions
(7)
Checking, in the case of an Enhanced Controller with a Fast I/O
Drivers fitted, the existence of Fast I/O references.
9.7.3. Error Messages #105 and #106 and I/O Scanning
9.7.3.1.
I/O Scanning
In a similar way to computing the sizes of data tables, so also, a GEM
80-400
Controller computes what I/O ought to be present from the addresses appearing
in the user program. The controller only attempts to read input data from, and
send output data to those I/O devices whose addresses appear in the program.
Refer also to the F-tables, F200 to F329, for further details. The rules that the
controller uses in its computation of which I/O table words to scan are given here:
9.7.3.2.
Basic and Verification I/O
Only those Basic and Verification I/O words appearing in the program are
included in the I/O scan. For instance, if the program contains a contact
referenced A1.0, the whole word A1 will be read from the input modules and
units. If a module is fitted and set it to an address that is not referred to in the
program, this module will not be scanned; no data will be read from or written to
it.