3 Data Exchange with the CPU Unit
3-2
CJ-series PROFIBUS Slave Unit Operation Manual for NJ-series CPU Unit (W510)
3-1 Input and Output Data
The CJ1W-PRT21 forms a link between two bus systems: the host CPU’s I/O bus and the PROFIBUS-
DP Master. The Unit can be considered as a slave to both systems: the I/O bus communication is con-
trolled by the host CPU Unit and the PROFIBUS-DP communication is controlled by a PROFIBUS-DP
Master.
Definitions
Being a slave of two systems may cause confusion as to which data should be considered ’input
data’ and which is ’output data’. In this manual all I/O data communication is defined from the point
of view of the PROFIBUS-DP system.
Slave INPUT Data is process data which the CJ1W-PRT21 reads from the assigned areas of the
host CPU. The CJ1W-PRT21 sends this data to the PROFIBUS-DP master unit.
Slave OUTPUT Data is process data which the CJ1W-PRT21 receives from the PROFIBUS-DP
master unit. The CJ1W-PRT21 writes this data to the assigned areas of the host CPU.
Slave Input Data
Slave Output Data
CJ1W-PRT21Host CPU PROFIBUS
Master
PROFIBUS
I/O Bus
CJ1W-PRT21Host CPU PROFIBUS
Master
PROFIBUS
I/O Bus
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