Motorola DSP56000 Manual page 430

INSTRUCTION DESCRIPTIONS
MOVE MOVE
Move Data
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.
Note that the symbols used in decoding the various opcode fields of an instruction or par-
allel move are completely arbitrary. Furthermore, the opcode symbols used in one
instruction or parallel move are completely independent of the opcode symbols used in
a different instruction or parallel move.
MOTOROLA INSTRUCTION SET DETAILS A - 161