![parallel to serial converter timing parallel to serial converter timing](https://www.ibiblio.org/kuphaldt/electricCircuits/Digital/04392.png)
Clearly, a serial interface, that can have as few as two wires, is much more economical. It requires a parallel data bus, along with some control signals, to all of the remote locations. However, this configuration has a significant disadvantage. You would then program each DAC by simply doing a Write command to the appropriate I/O location. With parallel DACs, you could map each one into a memory mapped I/O location, as shown in the figure. Initially, you must decide whether to use serial or parallel DACs. My digital-to-analog converters have to be physically remote from the central processor and from one another. More significantly, board space is saved because serial interface connections require fewer PCB tracks. This makes it possible to package a 12-bit serial ADC or DAC in an 8-pin DIP or SO package. From a space saving point of view, serial converters offer a clear advantage because of reduced device pin-count. The key difference between serial and parallel data converters lies in the number of interface lines required. When a conversion is complete, the AD7892 interrupts the DSP, which responds by doing a single read of the ADC's decoded memory address.
![parallel to serial converter timing parallel to serial converter timing](https://www.allaboutcircuits.com/uploads/articles/serial-in-parallel-out-shift-register-waveforms.jpg)
The figure shows the AD7892 interfaced to an ADSP-2101. It should be evident that the serial interface, in this case, must be bi-directional.Ī parallel ADC, on the other hand, connects directly (or possibly through buffers) to the data bus of the processor it is interfaced with. The register's bits control such functions as selecting the channel to be converted, putting the device in power-down mode, and starting a conversion. In this example, the DSP's serial port is used to program an internal 5-bit register in the ADC. The DSP usually (but not always) supplies an additional framing pulse that is active either for one cycle at the beginning of the communication or, as shown (TFS/RFS), for the duration of the transmission. To distinguish the bits of the serial data stream from one another, a clock signal (SCLK) must be provided, usually by the DSP However, sometimes the ADC supplies this clock as an output. The data stream also includes three additional bits that identify the input channel that the AD7890's multiplexer is currently selecting. The 12 bits that constitute the conversion result are transmitted as a serial data stream over a single line. Also shown is the timing sequence that the DSP uses to communicate with the ADC. The figure shows an AD7890 8-Channel multiplexed 12-bit serial A/D converter (ADC) connected to the serial port of an ADSP-2105 digital signal processor (DSP). In doing this we will dispel some myths about serial data converters. Let's start by looking at how a serial interface works and then compare it to a parallel interface. What do I need to know to choose and use one?Ī. I need data converters to fit in a tight space, and I suspect that a serial interface will help. Ask The Applications Engineer-19: Interfacing To Serial Converters-I