Hi Everyone,
We are planning to use some S-series VIM2 cards for our project for TCP Modbus communication. I am a bit confused on exactly how many slaves can one card handle.
Books online states:
You can create as many as 16 datasets for each Serial Card port. These 16 datasets can be allocated to the serial devices in several ways. For example, you can configure one serial device with 16 datasets, or you can have 16 devices on the port with one dataset each.
In another chapter:
Each VIM is seen by the DeltaV controller as four DeltaV Serial Cards, allowing up to 128 serial datasets (with 100 registers per dataset) over 32 TCP/IP addresses and 128 Modbus addresses per VIM.
So does this mean that I can have 128 devices on a VIM card if I only use one dataset per device?
Or there is this limit of 32 addresses and I can have maximum 32 slaves?
Thank you,
Istvan
The VIM informtion is a little confusing, when mixed with the serial card limitiations.
So the VIM card has two limitaions:
It can connect to 32 IP addresses, and it is seen as maximum of four serial cards by DeltaV. The four serial cards gives rise to the other limitations.
DeltaV Limitations:
4 serial cards gives 8 serial ports.
16 devices or Data Sets per port
Total devices(or datasets) = 8 x 16 = 128 devices or datasets of 100 registers (max of 16 bits/registers)
However the VIM limits you to a maximum of 32 devices, so the maximum for one VIM is:
32 devices
128 Datasets.
BTW: If you are having trouble with number of devices, then you can use a concentrator to collect data from mutiple devices and appear as one device (IP address) to the VIM.
Regards
Chris.
In reply to Chris:
Just one additional note - if you are using two VIMs configured as a redundant pair, the maximum number of devices (unique IP addresses) it can connect to is reduced to 16 instead of 32.