RS-485 Troubleshooting
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From: RahulS on 25 Jan 2006 06:02 Hi, I am using Rabbit development board which has separate ports for RS232 and Rs485. Right now i am using a single port both as RS232 as well as RS485. The port works fine for RS232 signals but for RS485 signals, the differential output is not proper.I think there is some problem with the differential voltages. Please help.
From: karel on 25 Jan 2006 06:08 "RahulS" <rahuls(a)kpitcummins.com> schreef in bericht news:1138186965.580233.127170(a)o13g2000cwo.googlegroups.com... > Hi, > I am using Rabbit development board which has separate ports for RS232 > and Rs485. Right now i am using a single port both as RS232 as well as > RS485. > The port works fine for RS232 signals but for RS485 signals, the > differential output is not proper.I think there is some problem with > the differential voltages. Well if you suspect the differential voltages, have you taken a look at hem? An oscilloscope would be the most appropriate tool. But what makes you think it is the voltage levels? If you are using a proper driver chip with proper supply voltages, and only correct load on the RS-485 bus, why then should the levels go wrong?
From: RahulS on 25 Jan 2006 06:21 I am using SP483EN chip for RS485 signals. I used oscilloscope to test the differential signals. The signals were not differential in nature. When i short the CRO ground and RS485+, it works. When i monitor the waveform between RS485+ and GND, the waveform is correct. When i monitor the waveform between RS485- and GND, the waveform is correct.But when i monitor the waveform between RS485+ and RS485-, the waveform is incorrect. Could this be the case that the RS485 driver IC is not functioning properly Regards
From: Meindert Sprang on 25 Jan 2006 06:37 "RahulS" <rahuls(a)kpitcummins.com> wrote in message news:1138188073.191302.290970(a)z14g2000cwz.googlegroups.com... > I am using SP483EN chip for RS485 signals. I used oscilloscope to test > the differential signals. > The signals were not differential in nature. When i short the CRO > ground and RS485+, it works. > When i monitor the waveform between RS485+ and GND, the waveform is > correct. > When i monitor the waveform between RS485- and GND, the waveform is > correct.But when i monitor the waveform between RS485+ and RS485-, the > waveform is incorrect. How do you measure that? Not by clipping the probe on RS485+ and the ground clip on RS485- I hope? > Could this be the case that the RS485 driver IC is not functioning The only proper way of measuring this is by using a dual channel CRO, one channel on each RS485 pin and checking if the waveforms are eachothers' opposite. Meindert
From: RahulS on 25 Jan 2006 06:46
I have already done that, after which i was able to conclude that differential signals are not correct |