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Modbus TCP nomenclature is the same as for the Modbus over Serial line protocol, as any device which send out a Modbus command, is the 'client' and the response comes from a 'server'. [29] The ADU for Modbus TCP is officially called Modbus TCP/IP ADU by the Modbus organization [30] and is also called Modbus TCP frame by other parties. [3]
A null modem adapter. Null modem is a communication method to directly connect two DTEs (computer, terminal, printer, etc.) using an RS-232 serial cable.The name stems from the historical use of RS-232 cables to connect two teleprinter devices or two modems in order to communicate with one another; null modem communication refers to using a crossed-over RS-232 cable to connect the teleprinters ...
The only connector specified in the original RS-232 standard was the 25-pin D-subminiature, however, many other connectors have been used to save money or save on physical space, among other reasons. In particular, since many devices do not use all of the 20 signals that are defined by the standard, connectors with fewer pins are often used.
In telecommunications, RS-232 or Recommended Standard 232 [1] is a standard originally introduced in 1960 [2] for serial communication transmission of data. It formally defines signals connecting between a DTE ( data terminal equipment ) such as a computer terminal or PC , and a DCE ( data circuit-terminating equipment or data communication ...
RS-485 supports inexpensive local networks and multidrop communications links, using the same differential signaling over twisted pair as RS-422.It is generally accepted that RS-485 can be used with data rates up to 10 Mbit/s [a] or, at lower speeds, distances up to 1,200 m (4,000 ft). [2]
RS-232 connector (D-Sub DB-25 variant) Many communication systems were generally designed to connect two integrated circuits on the same printed circuit board, connected by signal traces on that board (rather than external cables). Integrated circuits are more expensive when they have more pins. To reduce the number of pins in a package, many ...
Data Terminal Ready (DTR) is a control signal in RS-232 serial communications, transmitted from data terminal equipment (DTE), such as a computer, to data communications equipment (DCE), for example a modem, to indicate that the terminal is ready for communications and the modem may initiate a communications channel.
Mark and space symbols (current directions in early telegraphy, later voltage polarities in EIA RS-232 and so on, frequency-shift polarities in frequency-shift keying and so on) Asynchronous start-stop signaling was widely used for dial-up modem access to time-sharing computers and BBS systems.