Advantech Data Acquisition Modules ADAM 4000 Manual de usuario descargar pdf (Pagina 406)

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Appendix E

Appendix E RS-485 Network E

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E.1 Basic Network Layout

Multi-drop RS-485 implies that there are two main wires in an segment.

The connected modules tap from these two lines with so called drop

cables. Thus all connections are parallel and connecting or

disconnecting of a node doesn’t affect the network as a whole. Since

ADAM modules use the RS-485 standard, and use an ASCII-based

commands set, they can connect and communicate with all ASCII-

based computers and terminals. The basic layouts that can be used for

an RS-485 network are:

Daisychain

The last module of a segment is a repeater. It is directly connected to

the main-wires thereby ending the first segment and starting the next

segment. Up to 32 addressable modules can be diasychained. This

limitation is a physical one. When using more modules per segment the

IC driver current rapidly decreases, causing communication errors.

Totally the network can hold up to 256 addressable modules. The

limitation for this number is the two number hexadecimal address codes

that know 256 combinations. The ADAM converter, ADAM repeaters

and the host computer are non addressable units and therefore are not

included in these numbers.

Figure E-1 Daisychaining

1 2 ... 401 402 403 404 405 406 407 408 409 410 411 ... 428 429

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