Electrical properties of AX-12A interface


i have a AX-12A. I found the manual at https://emanual.robotis.com/docs/en/dxl/ax/ax-12a/ an saw the diagram in chapter 5.4.2, but I don’t understand it.

  1. which side is RS485 and which side is TTL to AX-12A? I assume, right is AX-12A?
  2. I assume, the “MOLEX4P” represents the molex connector at the AX-12A. But on my AX-12A, I have only three pins. So, how it is wired actually?
  3. what does “TTL Level Multi Drop Bus” mean electrically? Is that open collector? Or what?
  4. Is “high” logically “true” or “false”?

Maybe someone has answers to my questions.

kind regards

I could be wrong but I don’t think there is an RS485 versions of the as-12a servos? Mine are all TTL (have 3 pins) Which is more along the line of section 5.4.1

Unless you have some of the RS485 like servos with 4 pins, you can ignore that other diagram.

As Kurt mentioned in the above reply, AX series does not support RS-485.
I’ll ping this error to eManual admin.

Yes, no RS485… that’s the reason for my asking.

let me express my question in another way:
I have a serial interface, and I can have RS232 and/or RS485, both with the usual signals, i.e. TXD, RXD, RTS, CTS, DTR, DSR, DCD, RI for RS232 and duplex wiring for RS485.
How can I connect my AX-12A to the serial interface, as simple as possible. My question focuses on the missing of a “direction” signal, at least non of the signals in RS232/RS485 is named in that way. Can I just take the RTS (“Reqest to send”)?


P.S.: there are some ready-to-use RS323 to TTL converter, usually with a MAX232 IC on, it (or RS485 with MAX485). Can I use one of those devices. If yes, how is the wiring?

If you are trying to convert TTL to RS-485, you may need additional board that will do the conversion.
Since the DIRECTION_PORT is directly controlled by the mcu, replacing it with RTS may work depend on your hardware design, but I cannot guarantee such modification.
Please also note that we have RS-485 version DYNAMIXEL from XM430 lineup.