In some applications, terminal strips were used in place of a connector. RS485Receive() clears bit PD5 to place the transceiver in receive mode, and RS485Transmit() sets bit PD5 to place the transceiver in transmit mode. If you are familiar with RS232, then you may already know a little bit about it. With RS485 communication distances of 1200 m are possible.Differential signal lines also allow higher bit rates than possible with non-differential connections. The people who designed the standard made an arbitrary decision with practical implications How big a load can the line driver see without the signal being attenuated too much. Many people just call them motor drives. One very common example in the automation world is remote control of VFDs or Variable Frequency Drives. When a device drives the line it sees the load presented by the other devices and the terminating (and biasing) resistors. I don't have practical experience of installing more than 32 devices on a trunk. It is faster and much more versatile than the older RS232.
Because of this, the resulting noise current is many factors lower than with an ordinary straight cable.Shielding-which is a common method to prevent noise in RS232 lines-tries to keep hostile magnetic fields away from the signal lines. Chassis and signal grounds are connected together to the digital ground (DGND) signal. There are a variety of ways the MOSI, MISO, SCK and /SS pins on your QVGA Controller can be connected. This allows standard point-to-point full duplex communications, as well as a multi-drop configuration with one master (a single QVGA Controller or a desktop computer) and multiple QVGA Controller slaves. 2. Peter says: January 8, 2009, at 2:20 pm (Edit) The Standard imposes the limit on the number of unit loads presented by the device and does not limit the number of devices. Devices will be linked together via a bus configuration as shown in the picture above. The picture shows the magnetic field lines and the noise current in the RS485 data lines that is the result of that magnetic field.
In the picture above, noise is generated by magnetic fields from the environment. The magnetic fields are allowed to pass, what is rs485 cable but do no harm. RS485 is however most popularly used in programmable logic controllers and factory floors where there are lots of electrical noise. Utilizing a series of dedicated interface devices, it allows PCs and industrial controllers to communicate. RS232 is an interface to connect one DTE, data terminal equipment to one DCE, data communication equipment at a maximum speed of 20 kbps with a maximum cable length of 50 feet. One of the main problems with RS232 is the lack of immunity for noise on the signal lines. Note that the master device outputs the clock synchronization signal SCK to the slave’s SCK which is configured as an input. The communications is asynchronous because no synchronizing clock signal is transmitted along with the data. In the straight cable, all noise current is flowing in the same direction, practically generating a looping current just like in an ordinary transformer.When the cable is twisted, we see that in some parts of the signal lines the direction of the noise current is the oposite from the current in other parts of the cable.
Just like it’s older brother RS232, RS485 is a form of serial communication. While shielding is not specified for RS485 systems, it can help in many instances. Without termination resistors, signal reflections off the unterminated end of the cable can cause data corruption. Noise is easily picked up and limits both the maximum distance and communication speed.With RS485 on the contrary there is no such thing as a common zero as a signal reference. Let’s talk about what we now know about RS485. Let’s say you were monitoring a water pump filling a vessel. With your RS485 network, you can remotely monitor and control that pump from a control center. All of this allows you to speed up the VFD that controls the speed of that water pump. RS485 avoids this issue which also allows for shielding of the cables to prevent noise. Differential signals and twisting allows RS485 to communicate over much longer communication distances than achievable with RS232. Users can utilize a longer cable, up to 1200 meters or 4000 feet. Moreover, if Serial2 is running full duplex at 4800 baud, any other interrupt service routine that takes longer than 100 µs is likely to cause a problem.