D
This response is just not right:
> That is you can connect several devices to the serial line. Where RS232 only allows to connect 2 devices with each other.
Modbus is a communications protocol that may be used on any communications medium. The original specification, known as Modbus RTU was specifically tied to EIA-232 and specifies the parity bit and the start and stop bits of that EIA standard.
Later implementations called for use of EIA 485 and allowed Multidrop slaves, but one master.
Finally, Modbus/TCP was specified allowing the same application layer protocol to be used on Ethernet or any communications medium (including wireless) in which the Network and Transport layers were defined with TCP/IP protocol. With Modbus/TCP, the distinction between master and slave has been retired.
Dick Caro
===============================================================
Richard H. Caro, CEO, CMC Associates
Certified Automation Professional (ISA)
7121 Avalon Drive, Acton, MA 01720
E-Mail: [email protected]
Buy my books at the ISA Bookstore:
Wireless Networks for Industrial Automation
Automation Network Selection
Consumers Guide to Fieldbus Network Equipment for Process Control
===============================================================
> That is you can connect several devices to the serial line. Where RS232 only allows to connect 2 devices with each other.
Modbus is a communications protocol that may be used on any communications medium. The original specification, known as Modbus RTU was specifically tied to EIA-232 and specifies the parity bit and the start and stop bits of that EIA standard.
Later implementations called for use of EIA 485 and allowed Multidrop slaves, but one master.
Finally, Modbus/TCP was specified allowing the same application layer protocol to be used on Ethernet or any communications medium (including wireless) in which the Network and Transport layers were defined with TCP/IP protocol. With Modbus/TCP, the distinction between master and slave has been retired.
Dick Caro
===============================================================
Richard H. Caro, CEO, CMC Associates
Certified Automation Professional (ISA)
7121 Avalon Drive, Acton, MA 01720
E-Mail: [email protected]
Buy my books at the ISA Bookstore:
Wireless Networks for Industrial Automation
Automation Network Selection
Consumers Guide to Fieldbus Network Equipment for Process Control
===============================================================
