berni80
Member level 2
RS485 Problem
Hi,
I recently buy an USB-RS485 interface to connect my PC to the device I'm debugging.
It's base on the Prolific bridge IC.. www.prolific.com.tw
Looking at the RS485 A&B signal (without my target connected) the signal appears like the attacked picture.
From the top to the bottom:
- A-B Differential signal (digital)
- A and B Signals (analog)
- A-B Differential signal (analog)
As you can see the are more than 2 different level and I can't see
the "eyes" of a typical differential transmission.
The link is working at low speed (<9600) but doesn't work at higher speed.
The line is very short and I shoud not have reflection problem..
I tried with 120ohm termination with out any results...
Has anyone experience with the 485? Do I need some kind of external polarization?
Hi,
I recently buy an USB-RS485 interface to connect my PC to the device I'm debugging.
It's base on the Prolific bridge IC.. www.prolific.com.tw
Looking at the RS485 A&B signal (without my target connected) the signal appears like the attacked picture.
From the top to the bottom:
- A-B Differential signal (digital)
- A and B Signals (analog)
- A-B Differential signal (analog)
As you can see the are more than 2 different level and I can't see
the "eyes" of a typical differential transmission.
The link is working at low speed (<9600) but doesn't work at higher speed.
The line is very short and I shoud not have reflection problem..
I tried with 120ohm termination with out any results...
Has anyone experience with the 485? Do I need some kind of external polarization?
