Specifications
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2.2.3 Communication using random access buffer
A PLC CPU can communicate with a personal computer using the random access
buffer in the buffer memory of the Ethernet module.
When the data size is too large for the fixed buffer communication (up to 1k words of
data), the use of the communication through the random access buffer enables
sending/receiving a large amount of data.
(1) Utilizing as the common memory for the PLC CPU and external devices
Data of larger size (up to 6k words) can be exchanged with the external devices.
In the random access buffer, data can be freely written to and read from any
external device (*1) without fixing access to a specific external device.
Thus, it can be used as a common buffer area for all of the external devices
connected to the Ethernet. (*2)
*1 The communication function using the random access buffer cannot be used
for the communication between PLC CPUs.
*2 Reading/writing from the PLC CPU to the random access buffer is performed
asynchronously with reading/writing from external devices.
PLC CPU
TO instruction
FROM instruction
Ethernet module
Buffer memory
Random
access
buffer
Write
Read
Write
Read
External
device
External
device
(2) External devices capable of exchanging data
The communication using the random access buffer can be performed with the
following external devices.
1) External devices that are connected to the same Ethernet as the Ethernet
module
2) External devices that are connected to other Ethernet networks via routers
Personal computer
Router
PLC CPU (Access station)
Personal computer
Ethernet-2
Ethernet-1
2)
1)