RS-485 troubleshooting

I have read some documentation about the RS-485, the thing that i noticed is that the RS-485 receiver compares the differential voltage between A and B
" A standard RS-485 Rx recognizes any differential voltage (Pin A – Pin B) > +200mV as a logic 1, and any
differential voltage below -200mV as a logic 0 "
so i tested it on my bench by having a MAX13487E (datasheet) as a master to poll the slave data from a MAX485 module(datasheet)

The voltage between A and B from the master before connects to the slave is = 3.129V
after connecting both of them, i tested the voltage between A and B and the result is 100.1mV which is far below 200mV, but the correct modbus data can still be poll. all voltage tested from an idle state.

i refer to this troubleshooting guide that the voltage between A and B should be at least more than 200mV in an idle state( LINK )

im confused by the voltage that is below 200mV but the data can still be read correctly, am i doing a wrong measurement?

Thanks before :slight_smile:

It sounds like you are using a multimeter. You need an oscilloscope to visualise the voltage levels when data is being sent.