Asynchronous, Synchronous and Interrupt Modes of Interfacing ADC

Asynchronous, Synchronous and Interrupt Modes of Interfacing ADC

Asynchronous Mode: In asynchronous type interface, microprocessor starts the conversion process by activating the start of conversion (SOC) signal of the ADC. Microprocessor then continuously checks the end of conversion signal from the ADC. ADC activates this signal when conversion process is over. On receiving end of conversion signal, the microprocessor reads the data present at the output of ADC. This is illustrated in Fig. 13.8.1.

Synchronous Mode : In asynchronous mode, the microprocessor waste time by waiting for the end of conversion signal. The conversion time of ADCs is in the range of hundreds of microseconds. Thus for every conversion cycle, this much time of the microprocessor is wasted. In synchronous mode, microprocessor executes certain instructions so that execution time of instructions is greater or equal to the conversion time, during conversion process. After execution of these instructions, microprocessor reads data from ADC without checking end of conversion signal. Here, microprocessor utilizes conversion time in executing a part of the program, thus increasing throughput.

Interrupt Mode : Many times, it is inconvenient to write instructions whose execution time is nearly equal to the conversion time. To overcome this difficulty we can use interrupt mode of interfacing ADC. Here, end of conversion signal from ADC is connected as an interrupt input of microprocessor. In this case, microprocessor continues instruction execution after initiating the conversion process. Whenever conversion process is completed, ADC activates EOC signals and microprocessor is interrupted. Microprocessor suspends its program execution, saves the program status and then executes the interrupt service routine (ISR). The interrupt service routine reads the data from ADC and returns program control to the main program.

Review Question

1. Discuss different modes of interfacing ADC to microprocessor.