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Computer with built in RS485 Ports


john.ward
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I have a PC with two built in RS422/485 Ports and am curious if there is a way to use them versus USB to RS485 adapters. I realize that I would probably have to build custom cables to connect them to my LOR network. Any feedback would be greatly appreciated.

 

JW

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Can I assume these are either industrial computers or you added a card to get them?

 

Off hand, they would likely work.  To your computer, the RS485 adapter just looks like a serial port.  Yes, you would likely have to build your own cable.

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The LOR cable is  4 & 5 are "A" and "B" on the 485 network, and 3 is LOR power Positive, 6 is LOR power Ground, 1,2, 7, & 8 are not used. (CAT 5 connectors).

 

For you the A and B are all you need (and a pair of 120 ohm resistors) (computer, and LAST controller on the network) MUST be daisy-chain type network NO star or "y" connections permitted.

 

what are your 485 serial connectors on the computer , DB-9, DB-25, or CAT5 ????

 

Greg

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I sure hope you have the pin-out diagrams for the ports, there are some differences in what type of 485 pinouts exist.

 

You will need to tie TX+ and RX+ together, and TX- and RX- together as a separate set, this will give you "A" and "B" respectively (or the opposite), technically TX+ should be "A" but I have seen other configurations.

 

LOR positive (pin 3), and ground (pin 6) (in the CAT5 cable) are for LOR's own internal use (to power motion sensors, directors, and such) and are NOT used in the PC connection.

 

 

You also might need to tie the other 4 pins used in full duplex 485 into "loopback" this should cause the "A" and "B" pair to function as a 2 wire system.

 

I can't remember the other four pins names at the moment, will dig some old books and post them when I find my serial pinout book.

 

Greg

Edited by a31ford
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