I need to connect a bunch of Mass Flow Controllers on a RS485 (TIA-485-A) multipoint bus. I will use Modbus protocol to communicate with the devices.

As specified on modbus.org (Specification and Implementation guidelines), the serial bus infrastructure in a multipoint Serial Line system is like this:

Modbus connectors

In my project, I would need only the Passive TAP (no Active TAP), because the length of my cables are around 10 cm.

From the mechanical point of view, 2 types of connectors are specified. The RJ45, and the D-shell 9-pin, as depicted below.

Modbus - serial bus infrastructure

My question is, what can I found on the market as Passive TAP with either RJ45 or D-Shell 9-pin connectors?

Something like this with RJ45/D-Shell instead M12 would be nice. enter image description here


2 Answers 2


Likewise, L-Com (http://www.l-com.com) makes a DB9 Y splitter, available on the web.

  • \$\begingroup\$ Excellent! It´s exactly what I was dreaming of. \$\endgroup\$
    – RawBean
    Commented May 22, 2014 at 20:11

There are RJ45 Y-splitters on the market, to be used for ISDN. These are completely passive and wired one-to-one.


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