Data Table
Chapter 3
330
Output image table words can be used for storage when the
corresponding input image table words are used for nonblock transfer
input modules. However, when there is a vacant I/O group or slot in the
I/O chassis, do not use image table words for storage. This will allow
room for future system expansion.
Bits 14-17 of a timer or counter preset word can be used for bit storage,
provided data is not transferred to the preset word by a Get/Put transfer
or the timer is not set for a 0.01 time base.
Unused input image table words should not be used for storage. They
are cleared to zero during each I/O scan.
Word 027 should not be used for storage. Many of the bits are used by
the processor for control functions.
File Storage
Files are located in consecutive word addresses in the data table. Usually
file storage should be immediately below the last timer/counter preset
address. Files can include their own unique addresses as well as duplicate
preassigned addresses. Therefore, files should be carefully entered on data
table documentation forms.
Sequencer tables, as with files, should be entered on the data table
documentation forms because they also may have their own unique
addresses and/or duplicate preassigned addresses. Moreover, sequencer
tables can be 1, 2, 3, or 4 words wide. This means that the number of steps
in a sequencer table must be multiplied by the number of words wide
(words per step) in order to obtain the total number of consecutive data
table words required by a sequencer table.
The following recommendations should be considered:
Do not inadvertently allow files to overlap other files or a data table
boundary.
Leave space for file growth. If addresses between files are used for
bit/word storage, the addresses can be easily reassigned elsewhere if the
need arises.
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