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6 hardware, are provided on the circuit board. Terminators and bias circuit resistors also place a load on the communication link. Thus in Table 9 6 , RTS1 is connected to CTS1, and DSR1 is connected to DTR1 and DCD1 onboard the QScreen Controller using zero ohm shorting resistors. The secondary serial port is connected similarly except that the onboard connection of RTS to CTS, and DSR to DTR are permanent. 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 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). From the QScreen Controller’s point of view, these three signals (TxD, RxD, and ground) are the only connections required to perform serial communications. The QScreen Controller does not differentiate between these. 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.

Using the primary serial port is easy. If you do this now, remember to move the QScreen Controller’s serial connector back to Serial Port 1, and to change the terminal’s baud rate back to 19200 baud using the "Comm" item under the terminal’s "Settings" menu. 1 running at the prior established baud rate (typically 19200 baud). You can operate the port at any baud rate up to 4800 baud; just specify the rate you want before the BAUD2 command. 1200 is the baud rate that you choose; you can specify any standard baud rate up to 4800 baud. Now select the "Comm" item in the "Settings" menu of the Terminal program, and click on 1200 baud (or whatever baud rate you selected in the command above). 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, and after the compilation is done, enter Mosaic Terminal by clicking on the terminal icon and use the "Send File" menu item to send GETSTART.DLF to the QScreen Controller. We’ll use code from the GETSTART.C program.

In fact, the program works the same as it did before, but now it is using the secondary serial port instead of the primary port -- and you didn’t even have to recompile the code! This configuration works for many SPI devices, including the optional battery-backed real-time clock. SPIE is a local interrupt mask that allows an interrupt to be recognized when an SPI data transfer has completed, or if a write collision or mode fault is detected. A mode fault occurs when the SPI senses that a multimaster conflict (MC68HC11F1 Technical Data Manual, p.8-7) exists on the network as explained above in connection with the /SS input. The serial bridge Data View visualizer has two panes. We recommend that you keep the faster Serial1 port as the default serial link as you work through the exercises in this book. The primary serial port, Serial1, is supported by the 68HC11's on-chip hardware UART (sometimes called a USART), and does not require interrupts to work properly.

Data translation between different machines can be performed with ease, and applications that communicate via the primary serial port can be debugged using the secondary channel. A jumper, J3, configures the primary serial port for either RS232 or RS485 operation. Some of these converters can convert from RS232 to both RS485 and RS422 however many standard models only has one of the protocols. Transaction history from POS will be recorded without any protocols. In a place where you are hindered by the electrically noisy environment, RS485 will be the optimal choice. 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. The RS232 protocol provides for four handshaking signals called ready to send (RTS), clear to send (CTS), data set ready (DSR), and data terminal ready (DTR) to coordinate the transfer of information. Many terminals and PCs, however, do rely on hardware handshaking to determine when the other party (in this case the QScreen Controller) is ready to accept data.

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