• Maximum cable length of an unterminated RS485, RS422 or RS232 network Web 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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