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Table 11 5 shows the connection diagram for a standard 9-pin serial cable. The combination of the cable impedances and/or termination resistors will load the network and can make communications unreliable. 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 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. Because the requirements of every multi-drop application are so unique, it is difficult to specify or design a software protocol that meets everyone’s needs. This raises the question of implementing a protocol for data exchange between the device and the computer, and often it is necessary to monitor the data that the software application sends to the device using the serial port. A filter driver intercepts all I/O requests issued by application.

The RS-232 driver (Maxim Part No. MAX242) can be tri-stated under software control. The QVGA Controller’s kernel software contains a complete set of high level driver routines for the Serial2 port, and these functions are summarized in the Control-C Glossary. The primary serial port, Serial1, is supported by the 68HC11's on-chip hardware UART, and does not require interrupts to work properly. We have built sophisticated instruments using the QVGA Controller that operate very reliably using multiple interrupts in addition to the software UART. 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. In each case, your QVGA Controller will be communicating at 19200 baud, and this baud rate will remain in effect until another BAUD1.AT.STARTUP command is executed, or until you invoke the Special Cleanup Mode as described earlier. 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. In this case, cable connections must be made to Serial 1 at pins 5 and 6 of the 10-pin Serial Communications Header.

This allows the processor that is master to control the input /SS pins of other CPU’s, for example. While these signals provide a data path, they do not provide hardware handshaking that allows the two communicating parties to let each other know when they are ready to send or receive data. The product allows you to customize the list of data being analyzed, and specify the type and form of the analysis. Device Monitoring Studio makes sure packets are correctly sorted and presented through a number of supported data visualizers. Serial port monitoring and data processing algorithms are extremely optimized in order to provide you with slick user experience and eliminate all negative impact on operating system performance, stability, computer resources consumption, and introduction of communication delays even at high non-standard data transfer rates. The QVGA Controller makes it easy to configure a multi-drop network of QVGA Controllers controlled by a single master desktop computer. To implement this multi-drop scheme, each slave keeps its RS-232 transmitter silent until it is addressed by the master and is given permission to transmit.

Note that the master device outputs the clock synchronization signal SCK to the slave’s SCK which is configured as an input. 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. Network topology refers to the arrangement of various nodes (such as computers, servers, what is rs485 cable switches) in a computer network. The design of RS485 is targeted towards it being tolerant and forgiving to noise and long cable runs with the twisted pair cable arrangement. The standard does not discuss cable shielding but makes some recommendations on preferred methods of interconnecting the signal reference common and equipment case grounds. The most widely used communication standard is RS232. RS485 is made for serial communication with high speeds, support for long distances, and support for multiple devices (slaves). The /SS (active-low slave select) signal enables data transfers by slave devices when it is active low.