Once the Bytes have been Exchanged > 자유게시판

Move the serial cable from the "Serial Port 1" connector to the "Serial Port 2" connector on the QScreen. 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. But before we dive deep into those SATA cable classifications, we need to have a look at what SATA actually means. 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. Chassis and signal grounds are connected together to the digital ground (DGND) signal. The primary and secondary serial communications ports are accessible through the QVGA Controller's 10 pin, dual row Communications Connector (H14) and through the individual Serial 1 and Serial 2 connectors. Configured as a master device, the 68HC11 transmits bytes via the "master out/slave in" pin, MOSI. 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.

Also, in the diagram, the master QVGA Controller’s /SS (slave select) is configured as an output. Most computers conform to IBM PC AT-compatible RS232 interfaces which use 9-pin D-Type connectors, consequently the QVGA Controller brings out its serial ports to two female 9-pin D-Type connectors. Most computers conform to IBM PC AT-compatible RS232 interfaces which use 9-pin D-Type connectors, consequently the QScreen Controller brings out its serial ports to two female 9-pin D-Type connectors. There are surface mount resistor pads on the QScreen that will allow you to bring out the secondary serial port to the Field Header on pins 5-6 or 7-8 as shown with the parentheses in Table 11-3. Pads are also available to bring out the RS485 signals to the DB9 Serial 1 Connector. While handshaking is still with us, it is usually best to disable it in software (if possible) and/or "loop-back" the pairs of signals (RTS to CTS, DTR to DSR, etc.) While RS232 was rumored to be on the "way out" with the advent of many of the new communications standards, it is still alive and well today. In addition there is no good way to add terminations resistors at the ends of a "star" network.

The dual communications channels also provide an easy way to link systems that communicate using different serial protocols. A typical RS485 network can operate properly in the presence of reasonable ground differential voltages, withstand driver contentious situations, provide reliable communications in electrically noisy environments (good common mode rejection using twisted pair cable, shielding provides additional protection), and support thirty-two or more (many IC manufacturers have 1/2, 1/4, 1/8 unit load devices) drivers and receivers on the line. In fact, you have been using it all along as you worked through the examples in this document. Much like RS232, RS485 doesn’t have an actual standard connector. An "Automatic Converter" (RS232 to RS485) will turn on the RS485 transmitter when data is detected on the RS232 port, and revert back into the receive mode after a character has been sent. 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. This cable is usually 24AWG. Category-5 cable will generally work well in most instances even though its characteristic impedance is 100 Ohms.

The receiver load impedence is 12K ohms (or higher) and transmitter "leakage" current is ±100µA (or less) in either the powered or unpowered state. 12V. A driver in the high impedence (off) state is able to remain in this state over the common mode range, whether power is applied or not. The receiver is able to respond to differential signal levels of 200mV over the common mode range. The DWOM bit (port D wired-or mode) should always be set to 0. Setting DWOM to 1 takes away the processor’s ability to pull the Port D signals high unless there is a pull-up resistor on each bit of the port. Any required SPI output signals must be configured as outputs by setting the appropriate bits in the Port D data direction register which is named PORTD.DIRECTION in the QED-Forth kernel. These steps greatly reduce the chance that the communicating devices might be damaged by contention on the SPI bus. Failure to stay within this range will result in, at best, signal corruption, and, at worst, damage to connected devices. While the standard only supports low data rates and short line length (50ft.) it is still widely used and, very useful in many applications.

If you loved this information and you would certainly like to get more information pertaining to what is rs485 cable kindly go to the web site.