![background image](http://html.mh-extra.com/html/omron/nt20/nt20_user-manual_744538198.webp)
177
Memory Tables and Bar Graphs
Section 5-2
5-2
Memory Tables and Bar Graphs
Displaying and Referencing Character String Memory Table Contents
Since the character-string memory table entries can be allocated to the words
in the PLC, the PLC can write data to the character-string memory table
entries or the initial values can be set when creating the screen data.
Automatic updating is performed to ensure that the currently displayed NT20
character string memory table contents and PLC word contents always match
each other.
There are two methods for referencing character string memory table entries
used for character string display, as follows:
• Direct specification
• Indirect specification
• Direct Specification
Direct specification is a method of specification in which the contents of
displayed memory table entries are directly correlated with the contents of
the allocated words.
• Indirect Specification (Direct Connection Only)
In indirect specification, even if the displayed data is a character string, the
display is correlated with a numeral memory table entry. The contents (nu-
merical value) of this numeral memory table entry are regarded as a char-
acter string memory table entry number and the contents of the table entry
with this number is displayed.
Up to 50 numeral displays and 50 character string displays can be speci-
fied on one screen by using indirect specification.
This specification method is a little complex, but it allows the display to be
changed more easily according to the circumstances. In the example above, if
1 were added to the contents of memory table entry 20 to give 52, the con-
tents of memory table entry 52 would be displayed instead.
The memory table entries used for display can also be allocated to areas in
the PLC, so that the display can also be changed in response to changes in
the data to be displayed (i.e., the contents of character string memory table
entry 51 in the example above).
However, in comparison with direct specification, indirect specification
requires more time for processing.
NT20
PLC
a b c d
a b c d
6
6
1
2
6
6
3
4
DM0100
Direct
specification
Character string
memory table entry 51
Allocated words
(character string memory table entry 51)
NT20
PLC
a b c d
0 0 5 1
a b c d
0
5
0
1
6
6
1
2
6
6
3
4
DM0100
Allocated word (numeral memory table entry 20)
DM0000
Allocated words (character string table entry 51)
Indirect
specification
Numeral memory
table entry 20
Character string
memory table entry 51
Summary of Contents for NT20
Page 1: ...Programmable Terminal Cat No V091 E1 01 NT20 USER S MANUAL ...
Page 2: ...NT series Programmable Terminal User s Manual Produced March 2007 ...
Page 3: ...iv ...
Page 5: ...vi ...
Page 9: ...x TABLE OF CONTENTS ...
Page 15: ...xvi ...
Page 21: ...xxii EC Directives 6 ...
Page 37: ...16 Before Operating Section 1 6 ...
Page 153: ...132 Transferring the Resource Data Section 3 11 ...
Page 185: ...164 Numeral Setting Section 4 8 ...
Page 267: ...246 Key to Programs Section 6 8 ...
Page 281: ...260 Specifications Appendix A ...
Page 285: ...264 Transporting and Storing PTs Appendix C ...
Page 303: ...282 Function Restrictions Depending on the Support Tool Appendix I ...
Page 307: ...286 Index ...
Page 309: ...288 Revision History ...