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Do not use an asterisk in front of
ARx variables
here, since this is not indirect addressing.
Examples:
mvmm AR3,AR5 ; sets AR5 = AR3
stm #5,AR2 ; sets AR2 = 5
ldm AR0,A ; sets A = AR0
Immediate addressing means that the numerical
value of the data is itself provided within the assemblyinstruction. Various TMS320C54x instructions allow immediate
data of 3, 5, 8, 9, or 16 bits in length, which are signifiedin the assembly language syntax descriptions with one of the
above symbols. The 16-bit form is the most common and issignified by
#lk . 16-bit immediate values always
require an extra instruction word and therefore take an extramachine cycle to execute.
An immediate data operand is almost always specified in
assembler syntax by prepending a pound sign (
# )
to the data. Depending on the context, the assembler mayassume that you meant immediate addressing anyway.
Examples:
ld #0,A ; sets A = 0
cmpm AR1,#1 ; sets flag TC = 1 if AR1 == 1; else TC = 0
Labels make this more complicated. Recall that a label in your assembly code is nothing more than shorthand for thememory address where the labeled code or data is stored. So does an instruction like
stm coef,AR2 ; sets AR2 = memory address of label coef
mean to store the contents of memory location
coef in
AR2 , or does it mean to
store the memory address
coef itself in
AR2 ? The second interpretation is correct.
Because the
stm instruction has only one form,
expecting a
#lk immediate operand, the assembler
does not care whether the label is prefixed with a pound signor not. Still, it would have been better for us to include
the pound sign in the above example for clarity.
Many instructions have several versions allowing the use of
different addressing modes (see
ld for a good
example of this). With these instructions, including thepound sign is not optional when specifying immediate
addressing. The only safe rule, then, is always to prefix thelabel with a pound sign if you wish to specify the memory
address of the label and not the contents of that address.
If you are not sure how a particular instruction has been
assembled, you can always examine the
.lst file
produced by the assembler, and compare the hexadecimal opcodeslisted to the left of the assembly instructions with the
assembly opcodes given in the assembly language manual(Chapter 4 of the
Mnemonic
Instruction Set reference).
In the modes called
direct addressing by TI, the
instruction opcode contains a memory offset (see the "dma"bits on page 5-8 of the
CPU and Peripherals reference) seven bits long, which
is combined with either the
DP (data pointer) or
SP (stack pointer) register to obtain a complete
16-bit data-memory address. This divides the data memory intopages of 128 words each.
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