I have a system that uses RS485 in full duplex (MAX489 IC)
The system contains 4 modules daisy chained together first one is the master. I am having problems receiving data sent from the slaves. Here are the details:
Master has 120ohm termination resistors across the TX+/TX- lines and RX-/RX+ lines
Last unit in the chain also has these two termination resistors. The other two units do not have any termination resistors.
If I have just Master and Last Unit connected everything works great and I'm measuring 5v diff. signal across Master's RX-/RX+.
With 3 units (Master-Unit1-Unit3_Terminated) I get 3v diff. and everything still works fine.
With 4 units (Master-Unit1-Unit2-Unit3_Terminated) I get 1.9v diff and the MAX489 on the master does not recognize it as valid data.
I'm using CAT5 cable, 30ft between master and the next unit and 5ft cables between the units. Data is sent at a slow 9600bps.
My understanding was that MAX489 devices can drive up to 32 devices on a single line....
Please help.
The system contains 4 modules daisy chained together first one is the master. I am having problems receiving data sent from the slaves. Here are the details:
Master has 120ohm termination resistors across the TX+/TX- lines and RX-/RX+ lines
Last unit in the chain also has these two termination resistors. The other two units do not have any termination resistors.
If I have just Master and Last Unit connected everything works great and I'm measuring 5v diff. signal across Master's RX-/RX+.
With 3 units (Master-Unit1-Unit3_Terminated) I get 3v diff. and everything still works fine.
With 4 units (Master-Unit1-Unit2-Unit3_Terminated) I get 1.9v diff and the MAX489 on the master does not recognize it as valid data.
I'm using CAT5 cable, 30ft between master and the next unit and 5ft cables between the units. Data is sent at a slow 9600bps.
My understanding was that MAX489 devices can drive up to 32 devices on a single line....
Please help.