A couple of weeks ago I reported about a new type of RGB-LED with integrated controller, the APA102. One of the interesting new features of this device is a two-wire SPI interface instead of the proprietary one-wire protocol of the more common WS2812. Many microcontrollers have hardware SPI functions, which allow easy control of these LEDs, as opposed to timing critical bit banging. But it turned out this was not the end of the story. As pointed out by Bernd in a comment, there is some discrepancy between the datasheet and the actual behavior of the devices when it comes to the “end frame”. Reason enough to subject the APA102 to more scrutiny.
The diagram below summarizes the APA102 protocol as found in the data sheet.