이름 : Ervin
이메일 : ervin.hope@bigpond.com
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예식일 : Right here Is a technique That Helps RS485 Standard
문의내용:

No one solution can fit all installations. Consider three different installations. MODBUS, SNMP, MBUS, 1-Wire and SQL databases and system "plug-in" fully configurable, does not require programming.Access to hardware naprane. Data Access SQL / FTP / HTTP through. Improved access to hardware resources - efficient data access to multiple applications. The entire subject of handshaking is obsolete with modern USB to RS-485 adapters since the PC's driver's and/or hardware handle driver enabling, and a modern PC can handle data rates much faster than can be transmitted over an RS-485 network. The driver must output between 5V and 15V in magnitude into a load of 3kΩ to 7kΩ. The driver must not be able to output more than 100mA when shorted to any other conductor in the cable, must not be able to output more than 25V and must be able to handle an open circuit, or a short to any other conductor in the cable. These capacitors will act as a short to AC signals. A shield is sometimes used to reduce EMI in twisted pair, but will reduce the maximum RS-485 operational line length. There are no limits given in time units, so there is no minimum or maximum bit rate associated with RS-485.

It can drive things 1200 meters, which RS - 232 is about 15 meters maximum. Many people recommend wiring things up on a prototype with Category 5 cable connected as point-to-point full-duplex RS-485. The RS-485 circuit common is connected to earth ground in both PCs. The first is to connect the signal common of the driver/receiver circuit to "protective or frame ground" through a 100 Ω resistor. This frame ground is shown as being connected to the "green wire ground of power system", RS485 standard more commonly called earth ground. You can design the system to accomplish this if you pay careful attention to logic function of the driver being used, as well as the labeling of the terminal on the device. The standard defines the common-mode voltage as being referenced to ground, it defines a term "ground potential difference" as the difference in the signal ground between the driver and receiver, but it does not say that this is earth ground or just a a third wire common.

This helps to limit the current through the "third" wire. Anyone who has seen a device go up in smoke, is likely to be very vehement on how to, and how not to wire grounds. For each device interface, the driver and receiver are both connected to these two wires. The receiver is designed to operate with voltages between 3 and 15V in magnitude (i.e. both positive and negative voltages) but must be able to handle an input of 25V without damage. This means that low data rates can handle an improperly terminated (or even unterminated) cable better than high data rates. Slew rate limited drivers will improve signal quality significantly with an unterminated network. If so, these drivers could be RS-232 but could also be EIA/TIA-574. RS-232 typically has a transmit wire, receive wire and signal common wire. Some RS-232 to RS-485 converters originally used the handshaking signals such as RTS to control the enable of the RS-485 transmitter. Another problem with this scheme is that the transmitter needs to stay enabled during the transmission of all of the data.

In a computer system, SCSI-2 and SCSI-3 may use this specification to implement the physical layer for data transmission between a controller and a disk drive. Acuview allows for real-time monitoring, and remote metering access for PC based data logging using .xls, .csv, or.txt file formats. RS-485 is also used in building automation as the simple bus wiring and long cable length is ideal for joining remote devices. It is usually a fairly simple matter to reverse the wires and test the communications again. RS-485 supports inexpensive local networks and multidrop communications links, using the same differential signaling over twisted pair as RS-422. DH 485 is a proprietary communications protocol used by Allen-Bradley in their line of industrial control units. The WatchDog function ensures control of the operation of selected services at the hardware level. It may also have flow control signal wires. This does not mean the voltages will reach 0V or 5V on these wires.