rs485 voltage levels?

[jit_singh_tara]

rs485 voltage levels

whast does differential voltage of rs485 means .how is it different from rs232 voltage levels.

 

[nevans06]

rs485 voltage

Hi,

RS485 uses two wires to carry the single signal differentially. Both wires use 0 to 5 volts, with the two wires being driven opposite. The purpose of this is to provide noise immunity, because much of the common mode signal can be rejected by the receiver.

Take a look at the specification table here https://www.rs485.com/rs485spec.html
This should tell you what you need to know about the differences.

Regards,

Circatek Design Solutions
https://www.circatek.co.uk

 

[davidgrm]

rs485 levels

Rs232 uses (or should use) +12v -12v signals. rs485 uses 5 volt differential signal. In rs232 a 0 will be +12 and a 1 will be -12. This is only on 1 wire being the transmit line. On rs485 there are 2 transmit lines. One line goes to 5v and the other goes to 0. The idea is that the receiver will only accept the data if the lines are a 1 & 0 or a 0 & 1. If an interference spike hits the data cable and both lines become a 1 or both become a 0 then the receiver will ignore the change

 

[melc]

rs-485 voltage

RS232 needs only 3 wires (TX, RX and GND) for a full duplex communication, RS485 needs at least 5 wires for the same thing (tx+, tx-, rx+, rx-, GND)

Max wire lenght for an RS232 is around 600-800m at 9600bps, max lenght for RS485 is 1Km for 32 ULs.

 

[jit_singh_tara]

rs 485 voltage

mr melc are you sure that rs232 can communicate to 600 - 800 m .

 

[FvM]

rs485 voltage differential

Max wire lenght for an RS232 is around 600-800m at 9600bps

According to EIA/TIA-232E specification, load capacitance should limited to 2500 pF, this is equivalent to 20 or 25 m cable. Having e. g. 80 nF would be a lot more! I also expect, that RS232 may still operate with that long cables, but probably with many transmission errors.