While the default baud rate of the primary serial port is 9600 baud, you can speed your communications and download times appreciably by switching to a faster baud rate. In fact, the program works the same as it did before, but now it is using the secondary serial port instead of the primary port -- and you didn’t even have to recompile the code! This chapter describes those drivers, and presents code that makes it easy to configure the SPI for different data transfer rates and formats. In order to increase the extent of the Modbus network, repeaters can be used; and signal amplifying and regenerating devices provided with two communication ports that transfer to each what they receive from the other. This topology offers efficient data transfer but can be disrupted if any single connection breaks, though redundancy protocols can mitigate this risk by providing alternative pathways for data.

Network topology refers to the arrangement of various nodes (such as computers, servers, switches) in a computer network. The advantage of such a multi-drop RS-232 network is that the communications are full duplex, with each communicating party capable of simultaneous transmission and reception of data. In this method, all nodes within the network share the same pair of communication lines. Although the devices would share the same network, what is rs485 cable communications would only be understandable by members of the same group. What made it such an advancement over RS232 was the fact that it could transmit not only a single device to device transmission, but also a communications bus to connect multiple devices at once. Given the availability of ready-made communications cables, it is not necessary to study or understand the following descriptions of cable connections. In order to avoid errors when many devices are connected, cables of the same colour should be used for all the connections to the terminals A and cables of the same colour should be used for all the connections to the terminals B of the various devices (e.g. white for A and blue for B).

They are often used for serial connections going to a terminal server in datacentres, for example. In some countries, inserting two cables into the same screw terminal is permitted. Each device has a communication port with two terminals, which are indicated for the sake of convenience as A and B. In these two terminals the communication cable is connected so that all the devices that take part in the communication are connected in parallel. The twin consists of two conductors that are twisted together. Sig- lines are twisted as twisting nullify the effect of electromagnetic noise induced in a cable and provide a much better immunity against the noise which allows the RS485 to transmit the data up to 1200m of range. Be sure to use a wire pair such as the blue and blue/white pair for the data lines and a third wire or pair twisted together for the common connection. Its speed is strictly defined at 250kBaud. No device bearing the DMX mark may use any other speed. B- ports are connected to the corresponding ports of the next device using twisted pair cables. If on the other hand each terminal can accept only a single cable, a proper branch must be created using three auxiliary terminals for each instrument to be connected.

In this case it is possible to connect the main inlet and outlet terminal directly to the terminals of an instrument without creating a branch. All the ‘A’ terminals must be connected together and all the ‘B’ terminals must be connected together respectively. The branches must be no longer than 1200 m! The main cable must be no longer than 700 m! The maximum number of devices that can be connected to a main cable is 32, including the Master. Using a repeater, the main cable is divided into different segments, each of which can be up to 700 m in length and connect 32 devices (this number includes the repeaters). On the other hand, DMX chose a nice round number at what was then the top of the range and added protections to avoid pick up of "ridiculous" frequencies, that we would now consider for actual data. It then pumps out the bytes pretty much in a similar fashion, grouped per "frame".