Following Kodu, the MicroCode language is defined in terms of pages, where a page has a list of rules, and each rule consists of a When section and a Do section, each with a list of programming tiles. The When section begins with a sensor tile, followed optionally by one or more filters on the sensor. The Do section begins with an actuator, followed optional by one or modifiers to the actuator.
The picture above shows a 1-page program that shows a happy face on the micro:bit screen when the A button is pressed and a sad face when the B button is pressed.
A sensor tile can refer to a hardware feature as simple as a button, a thermometer represented by a floating point (or fixed point) value, or an accelerometer with a set of possible events. A sensor could also refer to a GPIO pin, a timer, microphone, radio, or other means for the program to receive notification of a state change or an event. It is also possible for a sensor to refer to an internal program variable, modified by some other part of the user's program (self-notification).
In the program above, the sensor refers to a press/touch event, without reference to the particular hardware feature (see filters below).
Filters follow a sensor and specify conditions under which program execution can proceed to the Do section.
If no filters are present, each sensor tile has a default filter that determines whether or not execution
proceeds. For example, if the sensor tile refers to a press event, with no following filter, the default filter will recognize any the press of any button.
If, on the other hand, a filter following the press event specifies a particular
button (such as A or B, in the program above), execution will proceed to the Do only when the given button is pressed.
The picker menu above shows the range of micro:bit hardware features that can generate a press event.