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MELSEC-Q
3 SPECIFICATIONS
3.9 List of Applications and Assignments of the Buffer Memory
This section describes the buffer memory.
(1) Configuration of the buffer memory
A buffer memory consists of a user area and a system area, as shown below.
(a) User area
1) This is the area where users write/read data.
2) The user area consists of areas for storing setting values for data
communication, for actual data communication, and for storing
communication status and communication error information.
3) Data read/write to the user area should be performed following the
instructions in the corresponding detailed reference page.
(b) System area
This area is used by the Q series C24 system.
(2) List of buffer memory assignments
A buffer memory is configured with 16 bits per address.
Name, default value, etc. of each address of the buffer memory is shown in the
lists on the following pages.
1) Abbreviations in the target Protocol column
MC : MC protocol
Non: Non procedure protocol
Bi : Bidirectional protocol
2) Meaning of symbols shown in the target Protocol column
The following symbols are assigned to protocols related to the setting
values of a corresponding area and to areas used for controlled with user
settings, and indicate what kind of access is allowed to the area in question.
RW : Area where it is possible to read/write from/to the PLC CPU and
an external device.
R
: Area where only reading is possible from the PLC CPU and an
external device.
– : System area used by the system or area not used by the
corresponding protocol.
3) Meaning of symbols shown in the Registration allowed/not allowed
column
Indicates whether or not it is possible to use a value in the corresponding
area by registering it to the flash ROM of the Q series C24.
Allowed : Area that can be registered and used.
Not allowed : Area that cannot be registered.
IMPORTANT
Do not write data in the "System area" of the buffer memory.
If data is written to any of the system areas, the PLC system may malfunction.
Some of the user areas are partially system areas. Care must be taken when
performing read/write to the buffer memory.