EAW DSA230i, DSA250i owner manual 6c Example

EXAMPLE 4:

Looping occurs between both the Link and CobraNet connections.

CobraNet	ETHERNET
Source	SWITCH

PC	485	CM1	SLink
DSA PILOT
		DSA "A"
		PLink

485	CM1	SLink
	DSA "B"
	PLink

485	CM1	SLink
	DSA "C"
	PLink

485 CM1 SLink

DSA "D"

PLink

Figure 8.6.6c Example 4

8.6.7 AVOIDING STUBS AND CORRECT 120 OHM TERMINATION

A long stub or branch off of an EIA-485 bus can cause a significant impedance mismatch and thus reflections and degradation of the computer control signals. Stubs of several feet / 1 m or more are considered "long." Avoid using stubs. If a stub is necessary, keep it as short as possible to avoid communication problems.

Rule-of-thumb

You can avoid stub and termination issues by connecting no more than two EIA-485 cables at any one module. Turn on the termination switch only for the module with one EIA-485 cable connected to it. This will, by definition, be the one at the end of the cabling.

EXAMPLE:

This installation may have problems with the EIA-485 branch from DSAi "A" down to "B". If in close physical proximity, this cable can be replaced with a Link cable connection from "A" to "B". If this is a long distance, connect "C" to "B" instead of "A", as shown by the dotted line.

For either condition, the end of line termination is turned on only for "D". This is because "D" is at the opposite end of the daisy-chained EIA-485 cabling from the PC.

PC

DSA PILOT

485	CM1	SLink
	DSA "A"
	PLink

485	CM1	SLink
	DSA "B"
	PLink

485	CM1	SLink
	DSA "C"
	PLink

485 CM1 SLink

DSA "D"

PLink

Figure 8.6.7 Example

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