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1-5
Section
Communication Using the Memory Link
17
1-5
Communication Using the Memory Link
This section describes the “memory link” communication method, which is dis-
tinct from memory link in direct connection.
Reference
Use of the memory link can be enabled by rewriting the system program of the
NT620S/NT620C using the system installer.
1-5-1 Memory Link
In a memory link, communication with an NT620S/NT620C is executed from a
personal computer or FA computer using RS-232C/422A communication.
When memory link is used, the NT620S/NT620C has a memory area called the
“PT memory” which is treated as an area within a virtual PC. This means that
pseudo-direct connection can take place between the PT memory and the
NT620S/NT620C display elements.
By reading from and writing to the PT memory, the host can execute NT620S/
NT620C processing via the PT memory.
In addition, dedicated commands are available for reading and writing of fre-
quently used numeral memory tables and character-string memory tables.
Numeral
memory
table
PT memory
Lamp
Direct connection
RS-232C communication
or
RS-422A communication
NT620S/620C
Seen from the perspective of the NT620S/NT620C, when using the memory link
method it makes no difference whether the “object” communicated with in direct
connection is external or internal, and therefore screen data for direct commu-
nication can be used without alteration by merely changing the object of commu-
nication.
1-5-2 Differences with Respect to Direct Connection
There are the following two major differences between the memory link method
and normal direct connection.
a)With the memory link method, commands must be used for the final stage of
communications with the host. Because of this, in comparison with the direct
connection method – which can be used with almost no requirement for a
program – the burden on the host is much greater. However, because the
memory link method gives unrestricted access to the extensive functions of
direct connection from a variety of equipment capable of RS-232C/RS-422A
communications – such as personal computers and FA computers – it ex-
pands the range of use of the PT.
b)Since the PT memory is a single area, there is no division into different types
of area as there is in the actual areas in a PC; there is only one type of area. In
the memory link method, the PT memory is made a virtual I/O relay area.
Therefore, even when screen data is created, display elements must always
be allocated to the I/O relay area.
Summary of Contents for NT620C
Page 1: ...Cat No V033 E1 5 Programmable Terminals NT620S 620C OPERATION MANUAL...
Page 2: ...NT620S 620C Programmable Terminals Operation Manual Revised April 2001...
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