2014年3月31日 · the voltage difference between D+ and ground, and D- and ground must be in the range acceptable by the receiver. If they are not, you have a ground potential difference problem. To solve it, you can either reduce the difference, or find a receiver that can tolerate a higher difference. The voltage levels for RS485, from The RS485 design guid:

2021年1月19日 · The +7 and -5 is the common mode voltage tolerance. In fact that is quoted wrong as common mode range of RS485 is required to be -7V to +12V, which means that a 5V powered chips can still communicate if there is up to +/-7V voltage difference between grounds of two chips, so that a 0V/5V signal on transmitter A wire is actually +5V/+12V signal ...

2023年5月28日 · The critical parameter is that the voltage between A and B should be greater than +/-200mV to be considered a valid logic level. Your schematic doesn’t show a gnd/0V reference between RS485 devices/nodes. The common mode voltage between nodes is …

2006年12月22日 · 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 ...

2023年5月12日 · The common mode voltage can be anywhere from 1-3V, and therefore your maximum voltage could be 3-4.75 V. What's important, is that after some voltage drop across your lines, the receiver still sees enough differential voltage to meet the conditions above.

2008年5月29日 · The "RS-485" levels shown in the said paper are at best typical voltage levels, but not actually related to the RS-485 specification, that mainly focusses on required differential signalling levels and maximum common mode voltage. That't the problem when referring to unqualified internet resources.

2020年1月14日 · 3) Supply voltage does not matter, if the return current still travels via ground wire between devices, creating a voltage drop. But if you a separate run supply return wire, you can use an isolated DC/DC converter at the remote end to create a local supply, and use a ground reference wire where no current flows between RS485 tranceivers.

2023年2月18日 · The absolute maximum rating of the MAX485 is irrelevant, as even if supply voltage would exceed 12V, the MAX485 will already be damaged, and even a 16V capacitor will handle some overvoltage (for example they might be tested to handle 250% of the rated voltage).

That's because the RS485 interface is outputting an idle condition i.e. B is the inverse of A because the transmitter is enabled. When idle, the lines A and B from the slave are both HIGH. This is because the slave is set to receive data and the RS485 chip has no control on the lines . External pull-ups are the likely cause of this.

2016年7月15日 · RS-485 has a defined differential voltage at both mark and space. The idle state is when voltage V_diff is -0.2V < V_diff < 0.2V; this is done by putting the transmitter in a Hi-Z state, usually by controlling the RTS signal from the UART. RTS is then used to turn on/off the transmitter, from Hi-Z to the defined voltage level for mark/space.