Maximum RS485 Cable Length Calculator
/Web calculator to help determine if a terminating resistor is required for an RS-485, RS-422 or RS-232 communication cable line. It calculates the maximum allowable network speed of a RS-485, RS-422 or RS-232 network based on network cable length and determines the maximum resulting Baud rate. Signal travel time and whether a terminating resistor is required for stable network operation are also calculated. For RS-232 lines, the length limitation is usually based on the local EMI interference levels since differential signal is not used like with RS-485 and RS-422 which are much more immune to interference signals. It is assumed that proper twisted pair cable is used for communication lines in all cases.
Output calculates the following parameters:
Baud rate (Bd)
Bit rate (bps)
Baud length pulse width (μs)
If a terminating resistor is required to absorb signal bounce from cable ends?
Byte rate (Bps) and MB/s and MB/min
The above outputs are calculated based on the following input parameters most of which the user does not have to enter manually:
Signal propagation velocity (Electrical signal speed in cable)
Signal propagation velocity
Network cable length
Signal travel time based on network cable length
Signal round trip travel time based on network cable length
Number of signal round trips for signal reflection to Damp Out
Time for signal reflection to damp out
UART controller sampling rate (Clock cycles per baud)
Baud length (Signal pulse width)
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