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Communications Using Memory Links Section 1-5
• The Programming Console and Device Monitor functions cannot be used.
• The following strobes of PT status notify bits do not turn ON (pages 7 to
27).
• Screen switching strobe
• Numerals input strobe
• Character-string input strobe
• The usable area for allocation is the PT memory only.
1-5-2 Comparison between Direct Connection and Memory Link
The major differences between the direct connection and the memory link are
as follows:
1,2,3... 1. In the memory link method, the communications with the host should be
carried out by using commands. Compared to the ordinal direct connec-
tion, which can be used requiring almost no programs, the memory link
method requires a program that is necessary for interchange of com-
mands.
This, however, gives advantages to the memory link method by using a
large variety of functions available in the direct connections from major
models such as a personal computer and a FA computer equipped with
RS-232C/RS-422A communications means, allowing the PT to be suited
for larger usage.
2. Actual PLCs have many kinds of areas, where as PT memory is a single
area with only one kind. When creating screen data by using the memory
link methods, it is always necessary to allocate display parts in the PT
memory.
For communications between the host and the PT by the memory link method
and for handling screen display elements, refer to the NT31/NT31C/NT631/
NT631C Programmable Terminal Reference Manual.
1-5-3 Memory Link Online Transfer Function
When memory link communications are being used, the NT631/NT631C can
be switched to Transmit mode from the host even if the NT631/NT631C is
operating and screen data can be written. (The NT631/NT631C can be
returned to RUN mode after the screen data is written.)
The memory link online transfer function can be used to replace screen data
at a fixed time each day or replace screen data with maintenance screen data
for maintenance.
For more details on the memory link online transfer function, refer to informa-
tion on the memory link online transfer function in the NT31/NT31C/NT631/
NT631C Programmable Terminal Reference Manual.