Table of Contents
Advertisement
Communication protocols
Modbus > Modbus Slave - Communication with the user program
6.4.7.1.1
Data consistency
78
n
Data transfer between CPU and CP happens block-by-block by the function blocks
FB 7 - P_RCV_RK and FB 8 - P_SND_RK.
–
Here the block size is about 32byte.
n
Data consistency is given only for a block size of 32byte.
n
For larger amounts of data, the data is transferred in the listed block size with a time
delay between each block. There is no consistency between these data blocks
because the data may be processed by the user program at the same time.
n
Access to the CPU memory area is carried out while the user program is running
whenever the FB 7 - P_RCV_RK is passed.
n
If data consistency is required when reading/writing registers or bits, the amount of
data transferred by a single message must be limited to 32byte.
n
For example a maximum of 16 registers with FC 03, 04, 16 or a maximum of 256bits
with FC 01, 02, 15.
n
Else you have to ensure the consistent processing of related data blocks by the user
program.
VIPA System 300S
HB130 | CP | 341-1CH01 | en | 18-40
Advertisement
Table of Contents
