An Introduction to Microcontrollers, Part Ⅱ

摘要

The previous microcontroller article explained how software can control digital outputs that turn LEDs - and other devices - on or off. The DIRA command set MCU pins as either inputs or outputs, and the OUTA command transferred a logic-1 or a logic-0 to identified output pins. You also learned about objects that perform operations independent of your code, and you used an object in the Timing.spin code to create a 1-second delay (see Table 1). That program also defined a byte (8-bit) variable, LEDCounter, that has 1 added to it each time through the repeat loop. Thus the value of LEDCounter can range from 00000000_2 to 11111111_2, or 0 to 255. You might have wondered what happens when a pass through the loop adds 1 to 255. The LEDCounter value becomes 0. Variables do not include a "carry" or an "overflow" bit, so although we know 255 + 1 = 256 (100000000_2), the 8-bit LEDCounter variable will hold only the eight least-significant bits - those eight on the right side of the value (underlined).