interfacing to microprocessor


Posted on Feb 7, 2014

The parallel interface transfers data 8 bits (or more) at the same time, using eight separate wires. It is essentially an extension of the data bus into the outside world. The parallel interface is ideal for inputting or outputting data from devices that are either on or off. For example, a single limit switch uses only one input bit, and an on-of


interfacing to microprocessor
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f signal to a motor requires only one output bit. These 1-bit signals are called logic variables, and eight such signals can be provided from a single (8-bit) port. This concept In other applications, the controller may use a parallel interface to connect to an analog device ”for example, driving a variable-speed DC motor. In such a case, the binary output of the controller must first be converted into an analog voltage before it can drive the motor. This operation is performed by a special circuit called a digital-toanalog converter. The digital-to-analog converter (DAC) is a circuit that converts a digital word into an analog voltage. It is not within the scope of this text to describe the internal workings of the DAC, but a general understanding of the operating parameters is appropriate. Figure 2. 5 shows the block diagram of a typical 8-bit DAC. The input is an 8-bit digital word. The output is a current that is proportional to the binary input value and must be converted to a voltage with an op-amp. A stable reference voltage (Vref) must be supplied to the DAC. This voltage defines the maximum analog voltage ”that is, for a digital input of 11111111, Vout is essentially Vref. If the input is 00000000, the Vout will be 0 Vdc. For all values in between, the output voltage is a linear percentage of Vref. Specifically, the output voltage for any digital input (for the 8-bit DAC) is An important consideration of...




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