Hello,

I am currently doing a project of a lightweight robotic arm and I am using Dynamixel RX-64 motors to control the movement. I am aware that the signal needs to be converted by using RS485. I would like to connect the RX-64 and RS485 together with the LPC 1768.

My questions regarding connections are as follows

1) If I were to control the movement of 2 RX-64 motors individually, do I still connect them in series?

2) Since RX-64 requires a 4 pin connector which have VDD, GND, D+, D- . Where do I connect D+ and D- and can both motor's D+ and D- connect in the same pin ?

Thank you

Eugene

At first read about rs485 at : http://en.wikipedia.org/wiki/RS-485

the RS485 is similare to rs232 except it's an half duplex protocol, but it's a bus protocol and needs only 2 wires (D+/D-) The way of how RS485 protocol works is quite simple.

You can put in parallele until 255 devices on the same bus.

One of the device is the master control (usually an microcontroller or a soft from a computer)...

The master sends an order (like serial) to every devices or to one that can be identified by an unique ID.

As all of the devices excepts the master are waiting for an order, every one can read the order sended by the master.

If one device has to get back an order to the master, it has to wait that the master give him the right to transmit on the 2 unique lines of the bus. But to use RS485 with your motors you need RS485 drivers chips as max485 from maxim.

you can have a look at http://aquaticus.info/rs485 to understand 485 better.

And the maxim site with a lot of datasheet : http://www.maximintegrated.com/en/products/interface/transceivers/MAX485.html#

best regards.

so to answer to your questions :

1- no not in serie, D+ and D- lines must be wired in parallel. 2- you need only 2 lines to drive the motors, you send datas to the motors through rs485. Each motor can have its own vcc and gnd.

and by the way that the RS485 is an symetrical signal, you don't need to use gnd between the drivers.