Advantech RS-485 user manual Basic Network Layout, Daisychain

Appendix C

C.1 Basic Network Layout

Multi-drop RS-485 implies that there are two main wires in a segment. The connected systems tap from these two lines with so called drop cables. Thus all connections are parallel and connecting or discon- necting of a node doesn’t affect the network as a whole. Since ADAM-5000 systems use the RS-485 standard and 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 systems can be daisychained . This limitation is a physical one. When using more systems per segment the IC driver current rapidly decreases, causing communication errors. In total, the network can hold up to 256 addressable systems. The limitation on this number is the two-character hexadecimal address code that can address 256 combinations. The ADAM converter, ADAM repeaters and the host computer are non addressable units and therefore are not included in these numbers.

	Setgment 1		Setgment 2
Coverter			Repeater
RS232/RS485			1
	RS-485
RS-232
1	2	N	1

Figure C-1 Daisychaining

ADAM-5000 C-3