Is there any standard DB9 pinout for the RS485 interface? If so please share the same.
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1\$\begingroup\$ Not that I'm aware of. Note that '485 can be used for many different function, from sending a single signal (like a reset) to a serial interface (like UART/USART) to muli-bit bus systems. \$\endgroup\$– SteveShCommented Jul 21, 2023 at 10:29
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5\$\begingroup\$ I vote to reopen. The question never asked for product recommendations or places to buy them. It simply asked if there is a standard pinout for RS-485 on DE9 and the answer is (a) No because RS-485 does not define that or (b) well maybe yes but there are multiple actual and just de-facto standards that use RS-485 or compatible interface on DE9 connector. \$\endgroup\$– JustmeCommented Jul 21, 2023 at 17:29
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3 Answers
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Connectors are not part of RS-485 standard.
As the old joke has it, standards are so good everyone should have their own:
Here are several conflicting specifications for half-duplex RS-485 on D-shell 9-pin connectors:
- Modbus uses pins 5 and 9 and 1. Standard, section 3.5
- Digi uses 3 and 9 and 5. Ref
- Virtual Serial Port uses 3 and 7 and shell. Ref, fig 3.9
If there's something common in your industry, use that. Otherwise I'd suggest Modbus, because "RS-485 on DE-9 per Modbus standard" is easy to say, easy to check, and buy ready-made cables for.
answered Jul 21, 2023 at 11:13
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2\$\begingroup\$ And NI has their version of RS485 where pins 4&5 (RX) and 8&9 (TX) are used, and many CAN devices use pins 2&7 (CAN cabling is largely compatible). Indeed, best to choose one based on what cabling is available. If the connector does not have to be DE9, there are even more common options available. \$\endgroup\$– JustmeCommented Jul 21, 2023 at 11:36
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No, because the RS-485 standard itself does not define any connector or any pinout, among many other things that the standard does not define.
Also a DB9 connector does not exist, but I will assume you mean DE9 connector.
However, many other standards that build on top of the RS-485 standard do define a connector and a pinout. So this means there can be many different pinouts used by many different standards on DE9 connector.
Just pick a pinout that is commonly used, standard or non-standard.
Many other differential buses that don't use RS-485 but still have rather compatible cabling and might use a DE9 connector in practice do exist.
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No. However I'd caution that lots of companies (computer manufacturers and others) have had desktop- or equipment-scale networks based on RS422 (daisychained) or RS485 (multidrop) and have claimed to have had standard connections, but at most that should be read as "standard for the equipment we manufacture and support, and anybody who wants to interface to it had better toe the line".
You will similarly find that communities, cartels or general "areas of application" will have standards, even if not blessed by ISO etc., and I'd suggest that adopting one or other of those as a wiring standard and documenting that e.g. "we expect cabling and connectors to be electrically compatible with Modbus" would be a good start.
