Файл: Introduction to Microcontrollers. Architecture, Programming, and Interfacing of the Motorola 68HC12 (G.J. Lipovski, 1999).pdf

Figure 4.27. FINDLBL Subroutine with Errors

27. Correct the assembly-language program in Figure 4.28. Do not change any lines that are already correct. This shortest subroutine LIST for "SA2" prints a line of the listing at the end of PASS2, after two bytes have been put into the object code. It prints the decimal line number ( < 10),the hexadecimal object code, and the source code. OUTHEX prints a binary number n in accumulator A as two digits (the hexadecimal representation of n). OUTCH places the ASCII character in accumulator A into a line of the listing, which is pointed to by the X register.

Figure 5.6. Loop Macro to Add Consecutive Values

letters to generate unique labels inside the macro itself. This capability is especially useful if a macro expansion has two or more "goto" labels in it; for without it, unambiguous labels could not be generated. Using the macro invocation number, each macro expansion generates labels that are different from the labels generated from the same macro that are expanded at a different time. For example, the macro in Figure 5.6, when implemented by ADD #M,N, adds the contents of the N bytes beginning in location M, putting the result in accumulator A.

A macro definition can use a macro defined earlier, or even itself (recursively). For macro assemblers that have conditional assembly, conditional directives within their definition can be used to control the expansion. The actual parameters of the macro can then be tested with these directives to determine how the macro is expanded. In particular, the IFC and IFNC directives can be used to compare a macro parameter, considered as a string, against any constant string. If a parameter is missing, it is a null string "\0." We can compare a given parameter, such as the second parameter, considered as a string denoted "\2," to a null string "\0." When the strings are equal, the second parameter is missing, so this condition can terminate the macro expansion.

The example in Figure 5.7 illustrates the use of recursion, conditional assembly, and early exiting of macros using MEXIT. You might want to use the ADDA instruction with a series of arguments, to add several bytes to accumulator A. If you wish, you can use a text editor to make copies of the ADDA instruction with different arguments. However, you can define a macro whose name is ADDQ, in which the body of the macro expands into one or more ADDA directives to implement the same effect. This ADDQ macro uses recursion to add one parameter at a time, up to eight parameters in this simple example, stopping when a parameter is missing (null string). When a null (missing) parameter is encountered, the macro "exits" by executing MEXIT, thereby not generating any more expansion or code.

ADDQ: MACRO

IFNC "\1",""

ADDA \1

ENDC

IFC "\2",""

MEXIT

ENDC

ADDQ \2,\3,\4,\5,\6,\7,\8

ENDM

Figure 5.7. Recursive Macro to Add up to Eight Values

PROBLEMS

1 . Give the SI and S9 records for the program in Figure 1.5.

2 . Give the program source code (in the style of Figure 1.5) for the following S- record: S10D0800FC0852FD0854137C08564E.

be the segments, with the same names; the sections are .data, .text, and .pgm; segment SRAM contains section .data; segment EEPROM contains section .text; and segment flash contains section .pgm. The starting address, named BEGIN, is to be put in $FFFE. The input file is to be progB32.o, and the output file is to be called progB32.abs.

5 . Write a parameter file for the 'A4. Its SRAM and EEPROM are to be the segments, with the same names; the sections are .data and .text; segment SRAM contains section .data; and segment EEPROM contains section .text. The starting address, named START, is to be put in $FFFE. The input file is to be progA4.o, and the output file is to be called progA4.abs.

6 . Write a parameter file for an expanded bus 'A4. Its internal SRAM, extended memory SRAM at $7000 to $7FFF, internal EEPROM at $4000 to $4FFF, and external ROM at $8000 to $FFFF, are to be the segments with the names ISRAM, ESRAM, EEPROM, and ROM; and the sections are .data , .edata, .text, and .pgm. Segment ISRAM contains section .data, segment ESRAM contains section .edata, segment EEPROM contains section .text, and segment ROM contains section .pgm. The starting address, named BEGIN, is to be put in $FFFE. The input files are to be camcorder1 .o, camcorder2.o, camcorderS.o, and carncorder4.o, and the output file is to be called camcorder.abs.

7 . Write a relocatable assembler program that uses fuzzy logic, that has a section .text that just calls fuzzy logic subroutines FUZZY and ADJUST one after another without arguments, and a section .pgm that has in it fuzzy logic subroutines FUZZY and ADJUST, which just have RTS instructions in them. Comment on the use of a relocatable assembler to break long programs into more manageable parts.

8. Write a relocatable assembler program that has a section .text that just calls subroutines OUTCH, OUTS, OUTDEC, and OUTHEX one after another. The argument in Accumulator A, for OUTCH, OUTDEC, and OUTHEX, is $41. The argument for OUTS, passed in index register X, is the address of string STRING1. A section .pgm has in it subroutines OUTCH, OUTS, OUTDEC, and OUTHEX, which just have RTS instructions in them, and the string STRING1, which is "Well done\r". Comment on the use of a relocatable assembler to break long programs into more manageable parts.