RS485 communications with thermostat wires

[frank_pan]

Hello everyone,

Just wanted to explore if the RS485 communications can be done with thermostat wires of 100 feet, which are not twisted pair type cable.  Does NXP have a RS485 driver chip to support this application?

Thanks a lot,

Frank

[diazmarin09]

Hello Frank,

I hope all is great with you.

As far as I know, the RS485 is popular for inexpensive local networks, multidrop communication links and long haul data transfer over distances of up to 4,000 feet. Please find further information here.

In this case, I would like to recommend the series below:

SC16IS752 / SC16IS762 – Dual UART with I²C-Bus/SPI Interface, 64 Bs of Transmit and Receive FIFOs, I...

The SC16IS752/SC16IS762 provides advanced features such as automatic RS-485 support. EFCR bit 0 (9-BIT MODE bit) is used to enable the RS-485 mode (multidrop or 9-bit mode).

More details about this issue on the Application Note AN10486: https://www.nxp.com/docs/en/application-note/AN10486.pdf

Because the RS-485 standard only defines the physical and data link layers with an addressing requirement, the application layer can adopt various proprietary or open communication protocols. Engineers can adopt existing protocols, such as Modbus, or they can define their own for their application.

So, the device supports the RS-485 standard and it is compatible with a RS-485 transceivers.

I hope this information helps.

Regards,

David

[frank_pan]

Thank you David very much for your info.  However my question was if it is possible to use thermostat wires (not twisted pair) for RS485 communications over .  Do you have any info to help with this question?

[diazmarin09]

Hello Frank,

Thank you for using the NXP communities.

Please accept my apologies for the misunderstanding. As far as I know, RS-485 uses two signal lines, ‘A’ and ‘B’, which must be balanced and differential. Balanced signals are two lines that share a pair in a twisted pair cable with the same impedance on each line. Along with matched impedance of the lines, there must also be matched impedance at the receiver and transmitter.

I personally consider that such thermostat wires might be useful for you as long as they share the same impedance. Unfortunately we do not have further documentation about it.

I recommend to perform some tests before.

Regards,

David

[frank_pan]

Thank you David for your suggestions.  I'm thinking to perform some test as I don't see any relevant discussions on this topic.

Frank