Texas Instruments TMS320C67X/C67X+ DSP 18. Data Types Supported by Ldbu Instruction 15-Bit Offset

LDB(U) Load Byte From Memory With a 15-Bit Unsigned Constant Offset

				Load Byte From Memory With a 15-Bit Unsigned Constant Offset
LDB(U)
Syntax					LDB (.unit) *+B14/B15[ucst15], dst
					or
					LDBU (.unit) *+B14/B15[ucst15], dst
					.unit = .D2
Compatibility					C62x, C64x, C67x, and C67x+ CPU
Opcode
31	29	28	27	23		22	18	17	13	12	9	8	7	6	4	3	2	1	0

creg

z

dst

ucst15

y

op

1 1 s p

3	1	5	15	1	3	1	1
Description			Loads a byte from memory to a general-purpose register (dst). Table 3−18
			summarizes the data types supported by loads. The memory address is
			formed from a base address register B14 (y = 0) or B15 (y = 1) and an offset,

which is a 15-bit unsigned constant (ucst15). The assembler selects this for- mat only when the constant is larger than five bits in magnitude. This instruc- tion operates only on the .D2 unit.

The offset, ucst15, is scaled by a left shift of 0 bits. After scaling, ucst15 is added to baseR. Subtraction is not supported. The result of the calculation is the address sent to memory. The addressing arithmetic is always performed in linear mode.

For LDB(U), the values are loaded into the 8 LSBs of dst. For LDB, the upper 24 bits of dst values are sign-extended; for LDBU, the upper 24 bits of dst are zero-filled. The s bit determines which file dst will be loaded into: s = 0 indicates dst will be loaded in the A register file and s = 1 indicates dst will be loaded in the B register file.

Square brackets, [ ], indicate that the ucst15 offset is left-shifted by 0. Parentheses, ( ), can be used to set a nonscaled, constant offset. You must type either brackets or parentheses around the specified offset, if you use the optional offset parameter.

Table 3−18. Data Types Supported by LDB(U) Instruction (15-Bit Offset)

		op				Left
						Shift of
Mnemonic	Field			Load Data Type	SIze	Offset
LDB	0	1	0	Load byte	8	0 bits
LDBU	0	0	1	Load byte unsigned	8	0 bits

3-126 Instruction Set SPRU733