Motorola 24-Bit Digital Signal Processor, DSP56000 manual Move Data, Move S,D

INSTRUCTION DESCRIPTIONS

	MOVE	Move Data	MOVE
Operation:		Assembler Syntax:
	S➞D	MOVE S,D

Description: Move the contents of the specified data source S to the specified destina- tion D. This instruction is equivalent to a data ALU NOP with a parallel data move.

When a 56-bit accumulator (A or B) is specified as a source operand S, the accumulator value is optionally shifted according to the scaling mode bits S0 and S1 in the system status register (SR). If the data out of the shifter indicates that the accumulator extension register is in use and the data is to be moved into a 24- or 48-bit destination, the value stored in the destination D is limited to a maximum positive or negative saturation con- stant to minimize truncation error. Limiting does not occur if an individual 24-bit accumu- lator register (A1, A0, B1, or B0) is specified as a source operand instead of the full 56-bit accumulator (A or B). This limiting feature allows block floating-point operations to be performed with error detection since the L bit in the condition code register is latched.

When a 56-bit accumulator (A or B) is specified as a destination operand D, any 24-bit source data to be moved into that accumulator is automatically extended to 56 bits by sign extending the MS bit of the source operand (bit 23) and appending the source oper- and with 24 LS zeros. Similarly, any 48-bit source data to be loaded into a 56-bit accu- mulator is automatically sign extended to 56 bits. Note that for 24-bit source operands both the automatic sign-extension and zeroing features may be disabled by specifying the destination register to be one of the individual 24-bit accumulator registers (A1 or B1). Similarly, for 48-bit source operands, the automatic sign-extension feature may be disabled by using the long memory move addressing mode and specifying A10 or B10 as the destination operand.

Example:

:

MOVE X0,A1;move X0 to A1 without sign ext. or zeroing

:

X0

Before Execution

$234567

X0

After Execution

$234567

A

$FF:FFFFFF:FFFFFF

A

$FF:234567:FFFFFF

A - 158 INSTRUCTION SET DETAILS MOTOROLA