Translations:Подключение внешних устройств/3/en

Here Vos is the transmitter bias voltage (measured relative to the common and midpoint of the voltage divider with the same shoulders connected to the A and B outputs), Vgpd is the voltage between the "common points" of the transmitter and receiver, Vnoise is the voltage of the electromagnetic " line, Vcm is the common-mode interference voltage applied to both inputs of the receiver, which adds up as Vgpd + Vos + Vnoise. The transmitter modulates the differential voltage, forming a signal. The receiver must recognize this signal in the presence of strong interference, and it does this very effectively, but within certain limits. The voltage values ​​for the transmitter and receiver are limited by the standard and range from -7 to + 12V (+/- 7V with respect to the 0..5V signal). In reality, in addition to interference, between the common points of the receiver and transmitter there may be a potential difference of the "ground" Vgpd, which is applied through the outputs of the shaper to the inputs of the receiver. In case of exceeding the Vcm of the above levels, communication becomes unreliable or even disappears. The induced interference is effectively suppressed by a screen grounded at one point. Interference through difference of potentials "common" points suppresses the third wire, closing the currents generated Vgpd, which otherwise would have been input currents lines A and B the receiver. The
As for the 2-wire circuit of the isolated RS-485, it is also unstable for the following reason. The system can be under parasitic induction in this case, but the current noise "general form" always eager to go back to the source, no matter where and how the chain captures interference, ie, including return through an isolated "general" scheme. This point can in turn become a source of electromagnetic interference for another part of the electronic circuit (for example, through capacitive parasitic links). A large explanation of the role of one wire is given only to save the user from the loss of valuable time for setting up communications. In addition, on long lines and at high exchange rates, it is recommended to use a matched cable (twisted pair on the screen, 120 ohm impedance) and termination resistors at the ends of the network segment.

Connection Diagnostics

First of all, after connecting the device and creating a connection, you can create a register in a known state, for example, the bit "always on", etc. After the register is created, its value (Value) will be displayed with the register list: