title: “Dr. Durant: CS-280: Sample Problems”
Standard: Write assembly code to convert a number from 0x00 to 0x0F stored in register A to an ASCII character code representing that character. Test your code in Wookie. Referring to page 71 of your pink book, note that the codes for character ‘0’ through ‘9’ and ‘A’ through ‘F’ are adjacent, but the code for ‘9’ is not adjacent to the code for ‘A’. Write this in C++ first, substituting an “unsigned char” (8-bit value) for register A; you will need a conditional statement to determine which of the 2 ranges your input is in. Just as you can write integer expressions such as “‘A’-3” in C++, you can write integer expressions such as “‘A-3” (only a leading quote for a character) in assembly. For documentation purposes, your final code should not use any explicit ASCII values; instead use ‘A, etc.
Standard: Write ASM code to evaluate the following arithmetic expression, where each variable is stored in a global memory location: f * g + h / i. Assume each value is an 8-bit unsigned integer and the result is to be of the same type.
Advanced: Write a subroutine that swaps the 16-bit return address on the stack with the value stored in a global variable and then returns. Put 2 programs in your .s file, one with the label _start, and another with the label _start2. Initialize the aforementioned global variable with the address of _start2. At one point, each program should bsr to the subroutine, which will return to the other. You should assume that your register values are changed when calling this subroutine (since the other main program might do so); also, this will not work if both programs try to store items on the stack (besides the return address via bsr). You have just written a simple, 2-process, non-preemptive multitasking operating system. A better operating system would need to maintain separate stacks and register values for each program (“process”).
Standard: Translate the following into assembly language, where each variable is a byte. Check your answer by using the HC11 GCC compiler…
byte j = 0x53; byte k = 0x39; byte l = 0x5A; k ^= j | l;
Standard: Prototype in C++ and implement in assembly a function that sends the 2’s complement of the value present on the PORTC pins (assume they have been configured for input) to port B, waits 100 ms, and then returns the 8-bit value present on port c.
Standard (ask for help on hardware setup, if needed): Using simple strobed input mode and the HC11 briefcase and experiment board, write a program that reads a 4-bit value from the DIP switches and displays the corresponding number between 0 and 15 on the 4-character display whenever one of the pushbuttons is pressed. Use the 4 MSBs of port C for input from the DIP switches. The display should retain the number until the button is pressed again, even if the DIP switches are moved to another configuration.
Standard: Design the key elements (hardware setup, output loop) of a program that uses handshaking output to send a list of 50 1-byte values to an external device. This device interprets each 8-bit value as a weight from 0 oz. to 255 oz. (15 lb. 15 oz.) and prints a label. Printing a label usually takes a few seconds, but sometimes takes longer as the label paper must be refilled. So, STRA will be a signal from the device to the HC11 specifying when the next piece of data can be sent. Specify what other information you need to know about the device in order to set up the handshaking I/O system and write the complete program.
Standard: Write a program that displays the analog voltage input to PORTE pin 3 on the experimenter board’s 4-character display. The number may either be displayed as a 2-digit hexadecimal number or as a decimal number between 0 and 255. The display should be updated approximately 8 times per second.
Standard: Using the integer division and/or multiplication instructions on the HC11, scale the sum of 4 successive readings of an A/D input to 16-bit integer in the range 0-50, 0-500, or 0-5000, each representing 0 V to 5 V with varying degrees of precision. Comment briefly on the accuracy of the least significant digit and the degree of bias in your integer calculation.
Modify your solution to the Week 6, Lecture 2 problem. Instead of monitoring the STAF bit yourself, enable the STAI interrupt and put the code that updates the display in your ISR. (The same vector is used as for the IRQ interrupt.) You will still be using simple strobed input mode, so the rules for clearing STAF are unchanged.