I'm wondering, Does assembler support if staments? (like a C program) Tried something very simple:
org 0h sjmp BEGIN org 50h BEGIN: IF R0 == #45 MOV A, #54 CPL A ELSE MOV A, #45 CPL A ENDIF END
Sergio, Yes, you can implement assembly IF statements using ASM macros, but they won't read like higher level if statements. Still the same, such macros for ASM51 are very useful and, if you code a lot of assembly, I'd recommend creating a "language extension" file that contains all of your useful a51 macros. Following is an example of just a few test/jump macros. Note, there's nothing magical about these; they simply consolidate some of the more commonly used opcode sequences. There's many other categories of macros that can be considered as well...namely DPTR related code sequences.
; IF x < y THEN GOTO addr ; jl MACRO x, y, addr clr c mov a, x subb a, y jc addr ENDM ; IF x <= y THEN GOTO addr ; jle MACRO x, y, addr clr c mov a, y subb a, x jnc addr ENDM ; IF x > y THEN GOTO addr ; jg MACRO x, y, addr clr c mov a, y subb a, x jc addr ENDM ; IF x >= y THEN GOTO addr ; jge MACRO x, y, addr clr c mov a, x subb a, y jnc addr ENDM jne MACRO x, y, addr mov a, x xrl a, y jnz addr ENDM je MACRO x, y, addr mov a, x xrl a, y jz addr ENDM
; If R0 <= B, then jump to MyJumpAddr ; jle R0, B, MyJumpAddr
jl MACRO x, y, addr [...]
A hint regarding all those macros: cjne is better for most of these than subb or xrl. In particular, you can easily get three exits from a single macro: one for a < b, one for a == b, and one for a > b. And the content of the accu at exit from the macro will be one of its operands, rather than their difference. Obviously, but CJNE doesn't accept just any operands. The macros as they're written, on the other hand, will accept any Rn, #data, or direct in either x or y parameter. True, they may not be as efficient as possible, but the couple of extra machine cycles is a small price to pay to have intuitive instructions that work for any type of operands.
Thank you Robert, that helped me a lot.
"True, they may not be as efficient as possible, but the couple of extra machine cycles is a small price to pay to have intuitive instructions that work for any type of operands." The implication behind the question is that the OP wants to use assembler because he believes it will be more efficient than 'C'. Thus, making the assembler inefficient to match the convenience of 'C' entirely defeats the object! This also serves to illustrate the fallacy of assuming that something written in assembler will inherently be more efficient than something written in 'C' - you can easily write inefficient assembler if you choose to (or if you don't have the skill to do otherwise). As Hans-Bernhard said, if you want the convenience of 'C' - then use 'C'!!
The implication behind the question is that the OP wants to use assembler because he believes it will be more efficient than 'C'. Thus, making the assembler inefficient to match the convenience of 'C' entirely defeats the object! This also serves to illustrate the fallacy of assuming that something written in assembler will inherently be more efficient than something written in 'C' - you can easily write inefficient assembler if you choose to (or if you don't have the skill to do otherwise). Its not like one would haphazardly sprinkle the "if" macros all over. They're simply useful comparisons instructions that replace commonly used code sequences and, if at all, sacrifice one or two machine cycles. Further, before one so quickly abandons assembler for C at the first requirement of convenience, one might consider there's a reason its called a "macro assembler" and take advantage of it...unless of course they lack the skill to realize this.