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CHAPTER 12 COMMUNICATIONS USING A FIXED
BUFFER
This chapter describes communications using a fixed buffer.
12.1 Applications
In communications using a fixed buffer, a programmable controller can actively send data; therefore, data can be sent
from the programmable controller to the host system when an error occurs in machine equipment or some other
conditions are satisfied. A maximum of 1K word of data can be sent or received between programmable controllers or
between a programmable controller and the host system.
12.1.1 Differences between the "Procedure Exist" and "No
Procedure" control methods
There are two control methods for communications using a fixed buffer; "Procedure Exist" control method and "No
Procedure" control method. This section describes the differences between the "Procedure Exist" and "No Procedure"
control methods.
A connection with a connected device is dedicated for "No Procedure" communications using a fixed buffer. MC protocol
communications and "Procedure Exist" communications using a fixed buffer and random access buffer cannot be performed
at the same time as "No Procedure" communications using a fixed buffer.
Item
Difference
Procedure Exist No Procedure
Message format Data is sent/received in a fixed data format.
Data is sent/received in the message format of the
connected device.
A response to data receiving A response to data receiving is sent. A response to data receiving is not sent.
Data code
Communications can be performed using a
binary code or ASCII code.
Communications are performed using only a binary
code.
Data length specified using a
dedicated instruction
Specified by the number of words. Specified by the number of bytes.
Amount of application data per
communication
Maximum of 1017 words Maximum of 2046 bytes
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