Chapter 12 Communications Using A Fixed Buffer; Applications; Differences Between The "Procedure Exist" And "No Procedure" Control Methods - Mitsubishi Electric QJ71E71-100 User Manual

CHAPTER 12
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.
Item
Message format
A response to data receiving
Data code
Data length specified using a
dedicated instruction
Amount of application data per
communication
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.
138
COMMUNICATIONS USING A FIXED
BUFFER
Procedure Exist
Data is sent/received in a fixed data format.
A response to data receiving is sent.
Communications can be performed using a
binary code or ASCII code.
Specified by the number of words.
Maximum of 1017 words
Difference
No Procedure
Data is sent/received in the message format of the
connected device.
A response to data receiving is not sent.
Communications are performed using only a binary
code.
Specified by the number of bytes.
Maximum of 2046 bytes