1 Features and System Configuration
1-16
CJ-series PROFIBUS Slave Unit Operation Manual for NJ-series CPU Unit (W510)
If it is necessary that each different set of transmitted data is acknowledged by the receiving side, the
user will have to implement a verification mechanism in the CPU programs on both the master and the
slave CPU. An example is to reserve one byte/word in the master’s data block for a transmission coun-
ter, which is copied back by the slave in its reply. The master may only transmit the next data if the
received counter value equals the sent value, indicating that the previous data was received by the
slave.
Consistency
The CJ1W-PRT21 guarantees consistency over the full length of the PROFIBUS data message, i.e.
all I/O data in one PROFIBUS message is transferred to the host CPU in one I/O refresh and vice
versa. There are added modules without consistency which simplify communication with Siemens
S7 masters.
PROFIBUS-DP Cycle Time
The overall PROFIBUS-DP communication cycle time will depend on the number and types of PRO-
FIBUS-DP master(s) and other slaves connected to the network, and the overall bus parameters
defined in the configuration of the master unit(s).
The time required to exchange I/O data between the CJ1W-PRT21 and its master will depend on the
number of input and output words defined in the master’s configuration, the selected baud rate and
on the performance of the master unit itself.
The minimum time interval between subsequent I/O data exchanges with the CJ1W-PRT21 (mini-
mum slave interval) is 0.5 ms as defined in the Unit’s GSD file.
A
B
C
D
Data read by host CPU
Data in slave output buffer
PROFIBUS master output data
I/O refresh
Master-Slave polling
E
F
A
D
F
C
A
B
C
D
E
F
