Electronics > Beginners
RS485 unterminated
<< < (4/5) > >>
rakeshm55:

--- Quote from: JS on July 06, 2018, 01:05:33 pm ---the source resistance by adding a series resistor to the source output

--- End quote ---

So if I connect 120 Ohms series resistance at the source the round trip reflection would cease to exist. Will it any way impact my slew rate and data transmission rate say I would like 15Mbps
JS:

--- Quote from: rakeshm55 on July 06, 2018, 05:15:34 pm ---
--- Quote from: JS on July 06, 2018, 01:05:33 pm ---the source resistance by adding a series resistor to the source output

--- End quote ---

So if I connect 120 Ohms series resistance at the source the round trip reflection would cease to exist. Will it any way impact my slew rate and data transmission rate say I would like 15Mbps

--- End quote ---
No, let's say the transmitter has an internal 120Ω resistor, you add an external 120Ω in series with it and at the other end now you need a 240Ω resistor instead of the 120Ω. In effect you have 3 times the resistance so 1/3rd of the power.

If you go up and up the capacitance of the bus starts to limit the bandwitdh, how much up could you go depends on that capacitance.

JS
rakeshm55:

Why cant I have a series termination (Source termination) and do away with parallel termination??
Since in my case its a single point to point connection cant I have a series termination??

As shown in attached diagram. Will it not eliminate reflections??

Please suggest
David Hess:

--- Quote from: rakeshm55 on July 07, 2018, 07:02:11 am ---Why cant I have a series termination (Source termination) and do away with parallel termination??
Since in my case its a single point to point connection cant I have a series termination??

As shown in attached diagram. Will it not eliminate reflections??
--- End quote ---

Series termination at the source without parallel termination at the load produces a reflection which causes the voltage to initially shift half way.
rakeshm55:
[quote author=David Hess link=topic=120854.msg1655066#msg1655066 date=1530960439

Series termination at the source without parallel termination at the load produces a reflection which causes the voltage to initially shift half way.
[/quote]
Thanks for pointing the issue....

This half way shift(1.5V) will remain for half of roundtrip time if i am not wrong....Also any voltage above 200mV will be considered as high....On similar lines any diff voltage below -200mV considered as low ... So wont this be ok..or will it be a show stopper....
Navigation
Message Index
Next page
Previous page
There was an error while thanking
Thanking...

Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod