1 FUNCTIONS
1.6 Communications Using the Random Access Buffer
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Physical address and logical address of random access buffer
This section describes the start address of the random access buffer of the RJ71EN71 or the RnENCPU (network part)
specified in the command.
The address specified for the random access buffer differs from the address specified by the external device and the address
specified with the FROM/TO instruction.
• Physical address: Address specified with program's FROM/TO instruction
• Logical address: Address specified by external device in start address item of command
Precautions
The following section lists the precautions for communications using the random access buffer.
Precautions for programming
■Initial processing and open processing completion
The initial processing and connection open processing must be completed.
■Send request from CPU module
Send cannot be requested from the CPU module. Completion of sending to CPU module is not checked. If the data send/
receive must be synchronized between the CPU module and external device, use fixed buffer communication.
■Random access buffer address
The address specified by the external device is different from the address specified with the FROM/TO instruction. For details,
refer to the following.
( Page 97 Physical address and logical address of random access buffer)
Data Format
The communication data is configured of the header and application data.
Header
The header is for TCP/IP or UDP/IP. The RJ71EN71 or the RnENCPU (network part) automatically adds and deletes the
header, the setting is not required.
■Details of header section size
The details of the header section data format and size are shown below.
• TCP/IP
• UDP/IP
020000
26143
6143
Buffer memory areas
Random access
buffer
Logical addressPhysical address
Ethernet (14 bytes)
IP (20 bytes)
TCP (20 bytes)
Ethernet (14 bytes)
IP (20 bytes)
UDP (8 bytes)
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