Omron NT31 Series, Operation Manuals

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Memory Tables
Section 7-3
S
Storage type and stored data
Internally, numeral memory tables store numeric values comprising eight signed
binary (or hexadecimal) digits. When the initial value or contents of the allocated
word(s) are stored in a memory table, the numeric value is interpreted in accor-
dance with the setting for “Storage Type” and is stored after conversion to signed
binary data. Accordingly, the same data will be interpreted in different ways by
the NT31/NT31C depending on the setting made for “Storage Type”.
Reference: Signed binary data expresses negative values as the complement of two (the bits
are inverted and 1 is added).
- Storage type for the BCD format
When using BCD format, the “Value” (initial value) and contents of the word(s)
at the host are interpreted as BCD (binary coded decimal) data. However,
since it is not possible to input a negative sign in a host word, the letter “F” at
the most significant digit is used instead to denote negative values (a negative
sign can be used in the setting for “Value”, so negative values can be input in
the normal manner for this setting).
If a value with a letter from “A” to “E” inclusive as its most significant digit, or a
value with a letter from “A” to “F” inclusive at any position other than the most
significant digit is stored in a host word, it is invalidated as illegal data and the
existing value is retained.
If the contents of a numeral memory table exceed the range that can be han-
dled by the allocated words of the host, the value is written to the host as “neg-
ative sign + less significant digits” (see below).
Contents of numeral memory table
(decimal notation)
Data at host Conditions
12345
→
2345
1 allocated word
−
1234
→
F234
1 allocated word
When using BCD format
123456789
→
23456789
2 allocated words
−
12345678
→
F2345678
2 allocated words
When using BCD format
- Storage type for binary format
When binary format is used, the initial value and contents of the host word(s)
are interpreted as signed binary data and are stored without change in the nu-
meral memory table.
With binary format, the most significant bit is the sign bit (when this bit is “1” it
indicates a negative value). When there is one allocated word, the most signif-
icant bit is bit 15; when there are two allocated words it is bit 31.
However, when the initial value is input using the Support Tool, the basis for input
is always the decimal system, regardless of the setting for “Storage Type”. The
“
−
” symbol can be input to indicate a negative value. If “$” is input at the head of
the input value, it will be input as a hexadecimal value (after confirmation of input,
it is displayed in decimal).