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INPUT AND OUTPUT (1/0) DEVICES

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INPUT AND OUTPUT (1/0) DEVICES Input/Output devices are the means through which the MPU communicates with "the outside world." The MPU accepts binary data as input from devices such as keyboards and analog-to-digital (A/D) converters and sends data to output devices such as LEDs or printers. There are two different methods b which an MPU can identify I/O devices :one uses an 8-bit address and the other a 16- bit address These methods are described briefly in the following sections. I/Os with 8-Bit Addresses (Peripheral-Mapped I/O) In this type of I/O, the MPU uses eight address lines to identify an input or an output device; this is also known as peripheral-mapped I/O .The eight address lines can have 256 (28 combinations) a dresses ;thus the MPU can identify 256 input devices and 256 output devices with addresses ranging from 00 H to FF H · The input and output devices are differentiated by the control signals I/O Read for input devices and I/O Write for output device...
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Advanced PIC18 Projects—SD Card Projects:Using the Card Filing System

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PROJECT 7.3—Using the Card Filing System The hardware of this project is the same as for Project 7.1 (i.e., as shown in Figure 7.8). In this project, a file called MYFILE55.TXT is created on the SD card. String “This is MYFILE.TXT” is written to the file initially. Then the string “This is the added data.. .” is appended to the file. The program then reads the contents of the file and sends the string “This is MYFILE.TXT. This is the added data.. .” to the UART, enabling the data to be displayed on the PC screen when HyperTerminal is run. The program listing of the project is given in Figure 7.12 (program SD3.C). At the beginning of the program the UART is initialized to 2400 baud. Then the SPI bus and the FAT file system are initialized as required by the library. The program then creates file MYFILE55.TXT by calling library function Mmc_Fat_Assign with the arguments as the filename and the creation flag 0x80, which tells the function to create a new file if the file doe...
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Counters and Timers

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Counters and Timers Many microcontroller applications require the counting of external events, such as the frequency of a pulse train, or the generation of precise internal time delays between com­puter actions. Both of these tasks can be accomplished using software techniques, but software loops for counting or timing keep the processor occupied so that other, perhaps more important, functions are not done. To relieve the processor of this burden, two 16-bit up counters, named T0 and T1, are provided for the general use of the programmer. Each counter may be programmed to count internal clock pulses, acting as a timer, or pro­grammed to count external pulses as a counter. Bit Symbol Function 0 IT0 External interrupt 0 signal type control bit. Set to 1 by program to enable external interrupt...
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