I have a SBC that has a RS-485 port. It has jumpers for bias and termination resistors.
I would like to connect one or two led character display units generally no more than 50 feet away. If using one display unit, I will simply connect the two devices point to point. If the installation calls for two display units, I would simply like to put a 'T' connector anywhere from 1 to 10 feet away from the first display to branch to the second. The display devices will be sealed and so I do not want to have to set any jumpers or throw switches and I only want one version of the display.
How should I terminate the display devices so they will work in either configuration? (This is not a one-time deal--there will be multiple installations of the system.)
Bill,
Thanks. I forgot to mention that because this will be a small character display, I can use a low BAUD rate, perhaps 9600. I guess I will use gain and termination resistors on the SBC side and nothing on the display side(s).
Thanks,
Dale
I already have some older display units built for RS-232. Since they are read-only (I only need to receive ASCII data at 9600 BAUD), do you suppose that I can simply feed in one of the RS-485 lines (-7/+12V) from my SBC--I can figure out whether A or B by trial and elimination--into the RS-232 RX receive lines (+/-15V)? for a quick and dirty conversion? The old unit uses the RS-232 serial input on a BS2. This is just to use up a few remaining units from the old stock.
Thanks,
Dale
On some verisons of the old Cricket schematic I used to include a pair of 1k resistors as a simple converter. It was for single ended RS232 to RS485 communications but didn't support any termination.
You could try a 1k resistor between RX & B-