Real World Instrumentation with Python

Data I/O: Acquiring and Writing Data

Now that we have some idea of what to expect in terms of the software we’ll need to interact with instrument hardware, let’s take a look under the hood and see how we can put it to work for us.

Basic Data I/O

When considering data acquisition, there are basically two types of data sources: external instruments, and data acquisition hardware installed in the computer itself. In both cases there is a transaction that occurs between your application software and the device. Sometimes the transaction is direct, such as when accessing the hardware registers of a device directly from the application-level code. This style of interface programming is rather rare nowadays, as the underlying operating system tends to prohibit direct hardware access by user-level code. In most cases, it will involve an intermediary such as a driver with a vendor-defined API (recall Chapter 5), or an interface library (e.g., pySerial).

When acquiring data from an external device, or sending data (e.g., a command) to a device, there are several ways to get there from here. If you want to send data, the first, and most obvious, approach is to just write the data to the port or device and let it go at that. When you want to read data, the obvious approach is to simply read the data on demand.

Both of these methods assume that when the device is sent a command or queried for data it will automatically and immediately perform whatever hardware functions are necessary to convert ...