This cable is usually 24AWG. Category-5 cable will generally work well in most instances even though its characteristic impedance is 100 Ohms. Ideally, the two ends of the cable will have a termination resistor connected across the two wires. In fact, you have been using it all along as you worked through the examples in this document. We have built sophisticated instruments using the QVGA Controller that operate very reliably using multiple interrupts in addition to the software UART. The Control-C Glossary contains a list of functions that temporarily disable interrupts, and the glossary entries give further information regarding how long interrupts are disabled. The primary serial port, Serial1, is supported by the 68HC11’s on-chip hardware UART, and does not require interrupts to work properly. A three-post jumper located between the third socket and H6 configures the primary serial port for either RS232 or RS485 operation. Connecting a standard full duplex link RS232 between two computers is the same as with a standard RS232 link, with the TxD (transmitter output) of each computer connected to the RxD (receiver input) of the other computer. The QVGA Controller offers a unique addition to full duplex RS232: it can place its RS232 transmitter into a high impedance silent mode under software control.
It provides a convenient means of connecting the QScreen Controller to a variety of peripheral devices, including analog to digital and digital to analog converters, real time clocks, and other computers which use high speed communication. If the /SS input to a slave is inactive (high), the slave ignores the SCK input, does not transmit or receive data, and keeps its MISO output in a high-impedance state so that it does not interfere with the SPI bus. In this situation, if the /SS input is pulled low while the 68HC11 is the master, what is rs485 cable the processor detects a “mode fault” (by setting a bit in the SPI status register) meaning that there is more than one master device on the SPI bus. 4. Built in defrost and defogging device. These steps greatly reduce the chance that the communicating devices might be damaged by contention on the SPI bus. In the most common multi-drop RS-485 protocol, one computer is designated as a “master” and the rest of the computers or devices on the serial bus are designated as “slaves”.
It does not specify or recommend any communications protocol; Other standards define the protocols for communication over an RS-485 link. Similarly, the RS-485 and RS-422 are among the most successful standards for industrial applications, however, it is often necessary to communicate between the standards. 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. Communications capability is essential for many instrument control applications. PTZ Cameras are commonly used in applications such as surveillance, video conferencing, live production, lecture capture and distance learning. The great thing about standards is there are so many to choose from. It is great solution for mobile surveillance. The value of each termination resistor should be equal to the cable characteristic impedance (typically, 120 ohms for twisted pairs). The value of each termination resistor should be equal to the cable impedance (typically, 120 ohms for twisted pairs). In general RS485 is designed for multi-drop, “daisy-chain” operation over a single twisted pair cable with a nominal characteristic impedance of 120 Ohms. Table 9-6 Serial Cable Connections. Table 11-5 Serial Cable Connections. Move the serial cable from the “Serial Port 1” connector to the “Serial Port 2” connector at the QVGA Controller.
To provide a convenient means of attaching two grounds to the serial cable, there are several pins (labeled DGND) on the communications connector that are connected to the controller’s ground plane. Figure 11 1 shows a typical multi-drop communications network. Table 11 5 shows the connection diagram for a standard 9-pin serial cable. A serial communications cable is supplied with QVGA Starter Kits. Given the availability of ready-made communications cables, it is not necessary to study or understand the following descriptions of cable connections. In this case, cable connections must be made to Serial 1 at pins 5 and 6 of the 10-pin Serial Communications Header. A serial cable accomplishs this connection. The QScreen Controller has two serial communications ports: a primary serial port called Serial 1 that supports both RS232 and RS485 protocols, and a secondary serial port called Serial 2 that supports RS232. When a slave is addressed, it executes RS232Transmit() at which point full duplex (two-way) communications commences between the master and the selected slave. This allows you to configure full duplex multi-drop networks in which a single master can sequentially address one of many slaves and start a full-duplex exchange of data. This allows the processor that is master to control the input /SS pins of other CPU’s, for example.
