CSE477 Assignment Notes for Labs 1 and 2

• There are two main ways the EVB may be programmed: directly by using the Buffalo assembler/disassembler or uploading assembled code (Motorola S-records).
  • In programming the 68HC11 directly, the assembler assumes all numeric values are in hexidecimal. Therefore, any base designators ($, %, d) will cause an input error with direct programming.
  • Writing code externally and assembling for upload provides for a less cumbersome programming environment. However, the assembler also has its quirks--white space must precede any instruction mneumonic regardless of the existence of a label. If a line begins with an instruction, the code will not assemble and errors will be generated.
• Timing for all instructions is given with the instruction descriptions in Appendix A of the Reference manual.
• The description and use of pseudo vectors in facilitating interrupts is covered in 3-5 thru 3-6 of the EVB User's manual and 3-17 of the reference manual. In short, each interrupt looks to a particular unchangeable address when it is handled. It is up to the programmer to place the opcode for a jump ($7E) followed by the starting address of the service routine to handle the interrupt.
• Because the Buffalo program handles interactive communication with the user, its interactive loop must be exited before another program can be run. After uploading an assembled program, the EVB must be reset (using the square red button) in order to exit the transfer loop used for the upload. Only after this, can you run your uploaded program.
• Pages 3-2 thru 3-4 of the EVB User's Manual contain invaluable information regarding utility subroutines that were included with the Buffalo program. OUTA (used often in EX10.ASM of lab 2) is especially useful in peppering buggy code with several "printf-like" statements to help in the debugging process. A program that wants to use this routine can simply use an EQUate statement for the starting address of the routines (all addresses listed on page 3-4) and a simple JSR to that routine will print out the character equivalent of the value in Accumulator A.
• A break point (maximum of 4) will cause the program to pause before that instruction is executed. Typing 'p' will resume normal program execution.
• The first program used in the labs (from 4-27 in the EVB User's Manual) is very valuable in showing basic serial communication techniques -- placing data in a transfer register and polling a status flag until the TxD Register Empty flag is set, etc..
• The EVB board uses an 8MHz crystal resulting in a 2 MHz bus clock. This value is needed in setting BAUD rates, as shown in Tables 9-1 and 9-2 of the Reference Manual.
• A pre-scalar is available in using input capture and output compare routines. Fast 16-bit rollovers at 2MHz make this an attractive option when slower timing is wanted and less precision is needed. Otherwise, some other routines must be introduced to handle timer overflow.