At 12:18 PM 9/7/2010, alan smith wrote: >Have a project that the client wants to replace a RS232 with RS485,=20 >pretty simple other than these two issues: > >1. direction control. Since the RS485 is 3 wire differential, the=20 >transceivers I have seen have direction control pins. However what=20 >happens if you don't want this...ie...several of the converters Ive=20 >seen do not see to require this for a point to point setup. I'm=20 >looking at one from FTDI and it uses a Exar SP481 and the two for=20 >direction control are floating. Check out Jan Axelson's wesite - she shows a nifty circuit for=20 dealing with RS-485 direction control. Its simple and effective in most ca= ses. >2. Addressing. The application may morph into a multidrop so I am=20 >thinking of putting a small PIC to be able to pass data that is=20 >addressed to the module. So I am looking for schemes, or=20 >references, on how the best way is to be able to identify itself as=20 >its plugged into the system. I will have control on the host side as well= .. There are lots of different techniques but one simple method relies=20 on each module being at some default address when it is new. The=20 master periodically pings that address to see if a new module has=20 been installed on the buss. If so, the master negotiates with the=20 new device, then tells it what address it should change itself to. Notice that this method works only when new devices are added to the=20 buss one at a time. You can't populate the buss with multiple new=20 devices, then power up the system and expect it to work. That's=20 because more than one device will respond to that default address. There are other, more complicated systems out there. dwayne --=20 Dwayne Reid Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax www.trinity-electronics.com Custom Electronics Design and Manufacturing --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .