Hi

I am developing a industrial PC-based Modbus app for the first time using VB.Net. I am currently reading 10 transducers using a USB-Rs485 converter. I would like to know if there is any advantage replacing it with a PCI Modbus Card. specifically, can the card offload the polling from the PC, and perhaps give me an event at specified period?

Regards
Alan

 

I'm surprised that you found a Modbus PCI card, I've never heard of one.

I've added serial cards to PCs to get additional serial network links, but a Modbus card? I suspect that you mean adding a serial RS-485 PCI card to move the hardware comm link to an internal card, rather than a USB converter.

If you mean adding an RS-485 serial card, then no, there's nothing on a serial card to 'give an event at a specified period'. The Modbus master software app in your PC is responsible for periodically polling the slaves for their data. RS-485 only carries the bits, it has no clue about what the bits mean or do. You've just exchanged one port for bit transfer with another port.

 

I never heard of a PCI Modbus card. there is a PCI Modbus+ card but it
is a completely different animal.

--
Bob

 

Hello,
If you have Modbus PCI card it is probably the Modbus Plus protocol card (SA-85). The Modbus Plus protocol is peer to peer protocol. If you have Modbus RTU devices on the net you can't use the MB+.

Regards
Andrzej
www.modbus.pl

 

Thanks folks. I got all the answers. Pardon my ignorance, I think I have mistaken a Modbus+ card for Modbus.

From you reply, there is no advantage in using a RS485 card other than noise interface, ease of product, etc.

I am not a control guy, though I have programming experience in industrial computers.

Thanks for your help.

Alan