Omron NT21 Series, Reference Manual

Page: 369 / 466

4-1 Section Operation of the Memory Link
360
4-1 Operation of the Memory Link
This section describes the function of the memory link. For outline of the function
of memory link, refer to
1-5 Communication by Using Memory Link.
4-1-1 PT Memory
With memory link, allocation of element bit or word is performed for PT memory.
The PT memory is a virtual PC area within the PT. The PT read/write to the inter-
nal PT memory and a host controls/monitors the PT by reading/writing PT
memory.
With PT memory, there is no classification of the area as there is with real PC
areas: it consists of a memory link area of just 10000 words from 0000 to 9999.
Memory link can be treated in exactly the same way as direct connections such
as host link and NT link, except that the channels to be allocated differ. The spec-
ification of bits is also the same.
A diagram of the PT memory is shown below.
Bits
Words
0000
0001
0002
9997
9998
9999
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Reference:
S
The PT memory is backed up by the battery even while the PT power is OFF.
S
The explanations in this section concentrate on the memory link communica-
tion method. For details on control and notification between the PT display ele-
ments and the PT memory, refer to
Section 2 PT Functions and Section 3 How
to Use the PT.
4-1-2 Memory Link Commands
When using the memory link, data is sent and received between the host and PT
using commands such as those indicated below.
Data Read Commands/Responses
These are the commands for reading the contents of the PT memory and
memory table in the PT. They are issued from the host and, as the response, the
PT sends back to the specified data
There are the following six commands.
•
PT memory read command Page 365
•
Numeral memory table read command Page 366
•
Character-string memory table read command Page 367
•
Bit memory table read command Page 368
•
Screen data comment read command Page 369
•
System status read command Page 370
Data Write Commands/Responses
These are the commands for writing data to the PT memory and memory tables
in the PT. They are issued from the host and, as the response, the PT sends a
reply indicating whether or not writing was completed normally. It is possible to
omit the response by a memory switch setting when writing is successful.
There are the following eight commands.
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