New developments USB – RS485

 

Well, it’s been a while since the last update so here it goes: we are preparing a few products which will be available in the shop, and as always the people that built them know them better. We’ll have a bit of a description of the manufacturing process going through all the required stages.

What will the products be?

Here it is : USB to RS485 adapter..

And the revised schematics:

SCHEMATIC USB-RS485

USB - RS485 adapter

And the test results are in..

Signal integrity test:

Test conditions:

Cable: 30 meters of twisted pair subsea grade cable 120 ohm terminated

Driver: USB-RS485 Adapter with the 120 ohm terminator jumper ON.

The character ‘U’ (ASCII 0×55) sent via a terminal (PUTTY) with 8 bits data, 1 start bit, 1 stop no parity

The baud rate was set for 115200 bps, 50000bps, and 1Mbps, the waveforms were captured with a 1Gs/s digital storage scope triggered on the start bit.

 

Character ‘U’ was captured on the scope at the far end of the cable (30m)

The speed is 115200 bps

 

A detailed view of a bit at 115200 bps

 

 

 

 

The bit rate was increased to 500.000 bps and the charaRS485_1Mbits_char_signalcter was sampled again.

 

 

 

 

This detailed bit view shows no sign of reflections on the falling and/or rising edges of the signal.

 

 

 

 

Finally the  view of  a 1Mbit/s signal over 30m of terminated cable.

 

 

 

Conclusion:
The signal integrity is maintained over 30m of twisted pair cable, terminated at both ends, driver and receiver. Signals are sampled on the far end (receiver side) with a digital storage oscilloscope at 1 Gs/s.
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