Assembly language programming: instructions and registers, reading inputs and writing outputs, branching and loops, delays, and the program development cycle (flowchart, code, assemble, test).

Program structure (up to 4 marks): the program loops forever. Each pass it reads the input pin (the switch), tests whether it is pressed, and branches: if pressed, it writes a high level to the output pin (LED on); if not, it writes a low level (LED off). In pseudocode: loop { read switch; if switch pressed then output high else output low; repeat }.

Decision instruction (up to 2 marks): a conditional branch (a compare-and-branch or bit-test-and-skip instruction) makes the decision: it tests the input bit and jumps to the LED-on or LED-off code accordingly.

Markers reward the read-test-branch-write loop structure, the LED on/off outputs, and naming the conditional branch (bit test and skip / compare and branch) as the decision instruction.

Delay loop (up to 2 marks): a delay is made by loading a register with a count and then decrementing it in a loop until it reaches zero (a "decrement and branch if not zero" loop). Each pass takes a fixed number of clock cycles, so the total delay is the count multiplied by the loop time; nesting loops gives longer delays.

Development cycle (up to 3 marks): plan the logic with a flowchart (or pseudocode); write the assembly code from the flowchart; assemble it (translate to machine code, fixing any syntax errors); download it to the microcontroller; and test it against the specification, debugging and refining until it works. Testing should be systematic, checking each input condition and output.

Markers reward the decrement-to-zero delay loop, and the flowchart-code-assemble-download-test cycle with systematic debugging.