Changing an Isel FB2 to LinuxCNC?

knipknap wrote:

I think a RS-232 to RS-485 adapter maybe would not work, because the (chain of) LS-173 uses full duplex (4 wire) RS-485, and I think RS-232 only does half duplex.

I am interpreting it as TX+ / TX- and RX+ / RX- differential pairs. I would expect a converter to do the TTL to differential conversion.

My initial confusion came from thinking I would have to translate G commands into servo driver commands in the HAL driver, which I understand now is of course not needed.

No, as you have probably realised, you just have to convert a velocity command that comes in on a HAL pin in to a formatted data packet. At least as a starting point. Handling the driver ID arbitration and setup will add incremental complexity, but that will come quite easily once the rest is there.

andypugh wrote:

Ah, I see! That makes sense now. Then I'll try the serial option - that would seem to be both the easiest and cheapest approach.

Thanks for all the help!

I'm going through old Logosol posts. I'd appreciate hearing where you are on this project.

You can communicate from a PC to a chain of Logosol drives with a USB to RS-485 converter. No Mesa ports to work with.
These converters typically use a chip like an FTDI for USB-to-UART conversion, plus an RS-485 transceiver (like a MAX485) to handle the differential signaling and half-duplex operation on the bus.
RS-232 vs RS-485:
RS-485 is half-duplex (not full duplex). It uses two wires (A/B or +/-) that are shared for both transmitting and receiving - devices take turns communicating on the same pair. RS-232 is full-duplex, using separate transmit and receive lines.
The key advantage of RS-485 is differential signaling, which eliminates common mode noise and allows much longer cable runs (up to 4,000 feet) compared to RS-232's typical 50-foot limit.
RS-232: Uses separate RX, TX, and GND lines. Single-ended signaling measures voltage relative to ground.
RS-485: Uses differential pairs (A/B or +/-). The receiver compares the voltage difference between the two wires to determine logic levels. Since noise affects both wires equally (common mode), it cancels out in the differential measurement, making the signal much more robust.