The Polling mode is implemented using SHORT_UPLOAD or UPLOAD commands. Each requested signal will be read from the ECU’s memory using a separate command. XCP commands are always processed sequentially meaning that first a command has to be processed and acknowledged before a following command can be send by the Master.
As a consequence, it is not possible to measure several signals exactly at the same time using the Polling mode. Signals are measured asynchronously with a time delay in between.
Measuring many signals in the Polling mode will lead to a significantly high bus load, since at least two XCP messages are needed in each cycle per measured signal.
In conclusion, the Polling mode is only suited for measuring less-dynamic signals at lower measurement rates, e.g. temperature variables. If you are wondering in which other scenarios the Polling mode turns out to be useful, feel free to ask this question the trainer of your upcoming CANape training.
In order to measure signals synchronized – meaning measured exactly at the same time, the DAQ mode has to be used. In the next chapter, you will learn about this second, more elaborate measurement mode.