Warning: What Is Rs485 Cable

The secondary serial port is connected similarly except that the onboard connection of RTS to CTS, and DSR to DTR are permanent. Designed with industry standards, it comes with a waterproof aviation connector to ensure that your connection will not be affected by the elements. 12 V and -7 volts will allow correct operation of the receiver. We can gain insight into the operation of the RS232 protocol by examining the signal connections used for the primary serial port in Table 9 6. The transmit and receive data signals carry the messages being communicated between the QScreen Controller and the PC or terminal. 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. To provide a convenient means of attaching two grounds to the serial cable, there are several pins (labeled GND) on the communications connector that are connected to the controller’s ground plane. This means that it is protected from contact with all dust particles, and also high-pressured water jets!

Let’s say you were monitoring a water pump filling a vessel. Let’s do a quick experiment to see how easy it is. Let’s talk about what we now know about RS485. The PLC is also connected to the VFD via RS485. RS485 main advantages as compared to other serial communication are tolerance to electrical noise, lengthy cable runs, multiple slaves in one connection, and fast data transmission speed. Function prototypes for this function and other versatile serial I/O routines are defined in the COMM.H header file, and are described in detail in the Control-C Glossary. Because all of the serial I/O routines on the QScreen Controller are revectorable, it is very easy to change the serial port in use without modifying any high level code. From the QScreen Controller’s point of view, these three signals (TxD, RxD, and ground) are the only connections required to perform serial communications. In this case, cable connections must be made to Serial 1 at pins 5 and 6 of the 10-pin Serial Header or pins 7 and 8 on the 24-pin Field Header. Given the availability of ready-made communications cables, it is not necessary to study or understand the following descriptions of cable connections.

If an interrupt service routine takes longer than 200 µs, then an entire serial bit will be missed, causing a communications error. If your application requires use of the secondary serial port as well as other interrupt routines, the key is to keep the interrupt service routines short and fast. Be sure to account for these effects when designing your application. If your application requires RS485, use the primary serial port (serial1) for RS485 communications, and use the secondary serial port (Serial 2) to program and debug your application code using the RS232 protocol. If you are running Serial2 at 4800 baud, the rest of your application must be able to function properly using the remaining portion of the CPU time. Thus, as a rough approximation, operating at 4800 baud full duplex requires about 40 to 50% of the 6811's CPU time (that is, an average of approximately 40 to 50 µs service time every 100 µs).

Routines that temporarily disable interrupts for significant periods of time can also interfere with the Serial2 port. The default serial routines used by the onboard kernel assume that full duplex communications are available, so you cannot use the RS485 protocol to program the controller. Although many applications use RS-485 signal levels, the speed, format, and protocol of the data transmission are not specified by RS-485. In the absence of signals, drivers don’t actively transmit 1s and 0s for receivers to detect, but they remain active and ready for the next signal. If you have already downloaded the program, you are ready to go. These detailed signal descriptions and cable diagrams are presented to provide complete information for those who have special communications requirements and for those who wish to make their own application-specific communications cables. Chassis and signal grounds are connected together to the digital ground (GND) signal. RS232 referenced ground to decipher the data it was transmitting. Although the RS232 protocol specifies functions for as many as 25 pins, each communications channel requires only three for simple serial interfaces: TxD1 (transmit data), RxD1 (receive data), and DGND (digital ground). However, note that the functions that write to EEPROM disable interrupts for 20 msec.

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