View Full Version : RS485 serial communication with LT1487

05-31-2010, 08:05 PM

I'm trying to get serial communication between two propeller chips via RS485 (two-wire). I have previously used the LTC 1487 with a Basic stamp, using the "Serout" command, with great success. I'm now trying the same chip with a propeller, but cannot make it work properly. I have so far tested with "Simple_Serial" object slightly modified, and it do transmit, but it's not the correct data (I use Parallax Serial Terminal for debugging the received transmission).

Is there a more suited object for this task, any suggestions?


05-31-2010, 10:20 PM
Have you tried tying DE/RE high (not via data pin) and then sending data? The next step would then be tying them low to see if you receive data properly. That then will at least confirm that the hardware and software are working together. Also, posting code and schematics is always helpful.

T Chap
05-31-2010, 10:59 PM
Can you post the code you are using? My experience with using 485 ad the prop was to make sure the enable was turned on and had a short delay between turning on and transmitting the data. If there were no delay between turning on the enable, the data was truncated. As well, there must be a delay to allow all the data to send before turning the enable back off. Schematics and code will help as stated above.

05-31-2010, 11:00 PM
Keep in mind that RS-485 chips require a bit of time to switch from receive to transmit mode, so a very short delay from that switch to the first byte may be required.

Jon McPhalen
Hollywood, CA

06-01-2010, 01:06 AM
Your suggestions concerning the transmit vs receive mode, and tying the DE/RE high etc, made me take a closer look at the connections I had made on the chip. And it was actually just a wire connection fault, sorry about this, isn't it just typical! I had connected the wire from the prop to DE instead of to the correct DI pin on the LTC1487 chip.

It's now working just fine, but I have so far just tested one-way communication and I will also take your advise concerning the delay issue to consideration when communicating (both tx and rx) with several nodes on the bus, later on in this project.

Thank you all for your reply!