Serial 8 servo controller

I have a serial servo ctrl 8, which I am tring to use to control an ROV.
The surface electronics are based on a 16f 877a sending data (minin SC mode at 2400 baud) through an RS 232 connector attached directly to a proprietry rs 485 transciever (the unbilical is 70 meters long). At the ROV end another rs 485 converts signals back to RS 232 for the servo 8 ctrl. The speed controllers work fine, however the problem is that I would like to transmint data back to the surface for heading. temp and depth (using an onboard 16f877a). If I break the transmit line on the servo 8 to the recieve line of rs 485 in order to send data back up to the surface the servo 8 ctrl’s orange LED stays on (not recieving a signal). Even if i connect the transmit lines up at the ROV end on the rs 485 the servo ctrl doesn’t work either. Does the servo ctrl perform some handshaking? Or any other ideas as to why it won’t work with out both TRX and RCX not connected?


I can’t quite tell what you are doing from your description, but there is no handshaking with the servo controller, and if the yellow LED is staying on after reset, that means there is no activity on the serial line at all.

- Jan

convertor.doc (24 KB)
I have added a bit map of the artwork for the connection of the servo 8 to the RS485 and tried to explain a bit more of what is going on.

I can’t tell much from that. It sounds like your line of questioning is almost entirely about the RS-232 to RS-485 adapter, yet you’ve given us almost nothing to work with regarding that adapter. Do you know how it’s supposed to work and that what you’re trying to do is supposed to work?

- Jan

The RS 485 is a line driver from better box model number 1009. I have spoken to them and I am going to try powering the driver directly as normally the unit gets power from the RS 232 connection.