Zilog EZ80F916 - Manual (Page 176)

UM014423-0607 Using the ANSI C-Compiler
ZiLOG Developer Studio II
eZ80Acclaim! ® User Manual
156
PSEUDOINSTRUCTION MACROS GENERATED BY THE C-COMPILER
A small number of pseudoinstruction macros are implemented in the C-Compiler so that
the compiler can more easily generate efficient assembly code. A pseudoinstruction has
the syntax of a single processor instruction, but it is actually a combination of two or more
processor instructions that work together. These macros are not primarily intended for use
by assembly coders; they are generated by the compiler and so sometimes can be seen in
compiler-generated assembly code. These descriptions are provided so that users can
understand the translation from these macros to actual assembly instructions. The follow-
ing pseudoinstruction macros are implemented in the eZ80
®
C-Compiler:
•
“UEXT HL (Unsigned Extension)” on page 156
•
“SEXT HL (Signed Extension)” on page 156
•
“LD BC,DE” on page 156
UEXT HL (Unsigned Extension)
This macro clears register HL so that later an 8-bit value can be moved to L, resulting in a
24-bit unsigned extension (into HL) of the 8-bit value. Register A is always used as the
source. The assembler translates this pseudoinstruction into the following sequence of
instructions:
OR A,A
SBC HL,HL
SEXT HL (Signed Extension)
This macro fills register HL with all 0’s or all 1’s depending on the sign bit (that is, bit 7)
of register A. This is done so that later moving the original value of register A into register
L will result in a 24-bit sign extension (into HL) of the 8-bit value in register A. The
assembler translates this pseudoinstruction into the following sequence of instructions:
RLA
SBC HL,HL
LD BC,DE
There is no actual eZ80
®
instruction to move data between 24-bit general-purpose regis-
ters. The assembler implements these pseudoinstructions with a sequence of
push
and
pop
instructions:
PUSH DE
POP BC