Once the Data has been Exchanged > 자유게시판

If the 68HC11 is initialized as a master (by setting the MSTR bit in the SPCR control register as explained below) then bit 5 of the Port D data direction register (DDRD) determines whether /SS is an input or an output. InitRS485() configures Port D to ensure that bit 5 is an output. 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. 19200 baud, select the "Comm" item under the "Settings" menu and click on 19200 in the "Baud Rate" selection box. 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. If you have not yet compiled the GETSTART program and you want to do the exercises here, open GETSTART.C in your TextPad editor, click on the Make Tool (the Make icon), and after the compilation is done, enter the Terminal Program by clicking on the terminal icon and use the "Send Text File" menu item to send GETSTART.DLF to the QVGA Controller.

Now select the "Communications" item in the "Settings" menu of the Terminal program, and click on 1200 baud (or whatever baud rate you selected in the command above). By connecting pairs of these handshaking signals together, the terminal or PC can be made to think that the QVGA Controller is always ready to send and receive data. This allows standard point-to-point full duplex communications, what is rs485 cable as well as a multi-drop configuration with one master (a single QVGA Controller or a desktop computer) and multiple QVGA Controller slaves. The QVGA Controller makes it easy to configure a multi-drop network of QVGA Controllers controlled by a single master desktop computer. 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. It is supported by virtually all personal computers, and is the default protocol for both of the QVGA Controller’s serial ports. 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.

B- ports are connected to the corresponding ports of the next device using twisted pair cables. In general it is very important not to run communications wires in the same trough or conduit or in parallel with AC power cables. Introduction Whenever you need to connect a storage device to a computer motherboard, you must have seen a bunch of ribbon or flat like cables being used for the purpose. The master computer broadcasts an address, a command code, a variable field and a checksum. When the 68HC11 controls the network, it is referred to as a "master"; otherwise, it is a "slave". By "isolating" sections of a large network, the accumulated noise on one isolated leg is not so likely to cause a data error that will propagate to another leg of the network. While it goes against conventional wisdom, and can potentially cause a problem with circulating currents by grounding a shielded cable at both ends, this method is very effective at keeping induced lightening noise away from the communications lines. 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.

The RS-232 driver (Maxim Part No. MAX242) can be tri-stated under software control. Because a mark (logic 1) condition is traditionally represented (e.g. in RS-232) with a negative voltage and space (logic 0) represented with a positive one, A may be considered the non-inverting signal and B as inverting. This type of multifunction instrument is ideal in panels where space is limited, in substation panels and in main industrial panels. Connect the shielding net to the main communication wire shielding and then ground it. If bit 5 of DDRD is 0, then /SS is an input. If bit 5 of DDRD is 1, then /SS is a general purpose output that operates independently of the SPI. 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.