1 FUNCTIONS
1.6 Communications Using the Random Access Buffer
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Communication structure
This section describes the mechanism of communications using the random access buffer.
Data flow
The following figure shows the flow of data communications using the random access buffer.
A dedicated packet is used to exchange data between the external device and the RJ71EN71 or the RnENCPU (network
part).
A program is used to access the random access buffer from the CPU module.
The process is executed asynchronously with the program, so if synchronization is required, use socket
communications or communications using the fixed buffer.
External devices capable of data exchange
Data can be exchanged with the following external devices.
• Devices in Ethernet to which the RJ71EN71 is connected
• Devices in Ethernet to which the RnENCPU (network part) is connected
• Device connected via router
Procedure for reading from external device
The following figure shows the processing when sending data from the RJ71EN71 or the RnENCPU (network part) in
response to a read request from the external device.
After the module parameters are set, check that the initial processing of the RJ71EN71 or the RnENCPU (network part) has completed normally. ('Initial
status' (Un\G1900024.0): On)
The open processing is executed to establish a connection between the RJ71EN71 or the RnENCPU (network part) and external device. ( Page 378
TCP/IP Communications, UDP/IP Communications)
The program writes the data into the random access buffer of the RJ71EN71 or the RnENCPU (network part).
The read request is sent from the external device to the RJ71EN71 or the RnENCPU (network part) asynchronously from the above processing. (RJ71EN71
or RnENCPU (network part) side: Receives command)
When the read request is received from the external device, the RJ71EN71 or the RnENCPU (network part) send the data written into the random access
buffer to the external device. (RJ71EN71 or RnENCPU (network part) side: Sends response )
The connection is closed when communication is finished.
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ACK (TCP only)
ACK (TCP only)
Response/data read
Read request (command)
Writing using the TO
instruction
CPU module
Random access
buffer
External device
RJ71EN71 or RnENCPU
(network part)
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