The differences between rs232 and rs485 serial communication...

[fateme91]

Hi
I need some information about these 2 communication differences.
forexample: what is it? driver load impedance.

thanks

 

[shaiko]

The biggest difference is RS232 being single ended while RS485 is differential.
Read this please:

https://digital.ni.com/public.nsf/allkb/2CABB3FD5CAF2F8686256F1D005AD0CD

 

[fateme91]

Do u know what it means? driver load impedance....

 

[shaiko]

I guess it's the output impedance of the Tx driver...

 

[ud23]

https://www.analog.com/static/imported-files/application_notes/AN-960.pdf

RS485 interface electrical specifications says

standard Driver load impedance is 54 Ohms max standard Receiver input impedance >=12K ohms,

RS-485 specifies a hypothetical term of a unit load (UL), which represents a load impedance of approximately 12 kOhms.

Drive capacity is 32 unit loads, i.e., 32 12kΩ receivers in parallel( gives 12k/32 = 375 Ohms). For receivers of higher input impedance, the number of unit loads on one bus can be higher. Any number of receivers can be connected to the bus, provided that the combined (parallel) load presented to the driver does not exceed 32 unit loads (375Ω).

The driver load impedance is 54Ω maximum, which, in a typical 24AWG twisted-pair environment, is 32 unit loads in parallel with two 120Ω terminators ( Parallel combination of 375 Ohms and 60 Ohms ==> 54 Ohms (approx).