An industrial pressure vessel is to be kept at a gauge pressure between 300 and 500 kPa. When the pressure falls below 300 kPa, an automatic valve is to inject steam. A human operator can press and hold a switch to inject steam, but not over 500 kPa.

Such an industrial process could be controlled in any of several ways, for example by old-style electromechanical relay logic (not treated in ECE 3254) or by a modern programmable logic controller (PLC, also not treated in ECE 3254). On the floor of an industrial facility, the PLC is the most likely to be deployed in practice, but let us suppose that this particular industrial process is controlled by a CPU12 microcontroller.

The multiplexer/demultiplexer (mux) connects the following devices to the microcontroller.

• A pressure gauge (address $0420). Digitally, the gauge reads 1 for 10 kPa, 2 for 20 kPa, 3 for 30 kPa, and so on. The gauge likewise reads -1 for -10 kPa, and so on. The gauge reads 0 between -5 and 5 kPa.

• The aforementioned manual switch (address $0430). Digitally, the switch reads 1 when the human operator is pressing and holding the switch. The switch reads 0 at other times.

• The aforementioned automatic valve (address $0450). A digital signal of 1 opens the valve, injecting steam. A digital signal of 0 closes the valve.

• A timer (address $0480). To set the timer for 1 second, a digital 1 is sent to the timer. To set the timer for 2 seconds, a digital 2 is sent, and so on. The timer starts timing as soon as it is set. When the timer expires, it interrupts the microcontroller. Sending a 0 to the timer cancels timing in progress.

Problem 1: in CPU12 mnemonics and machine language, using techniques of the lectures of April 4 and 9, write a program to run the steam-injection system.

Timing: poll the pressure gauge and/or manual switch every 5 seconds while the valve is closed; poll them every 1 second while the value is open.

Comments: to the right of your code, include sufficient English commentary that an engineer reading your program can understand what the various parts of the program do. You can assume that the engineer is familiar with the CPU12 but not that the engineer can easily understand a bare, uncommented mnemonic machine-code listing.

Problem 2: sketch a memory map and a system block diagram for problem 1.

There are only the two problems. However, problem 1 is not easy, especially if computer programming is not your forte, so allow adequate time. Ask the GTAs for help if you need it, 255 Whittemore, 10 a.m. to 6 p.m.