INSTRUCTION DESCRIPTIONS
MOTOROLA INSTRUCTION SET DETAILS A - 193
If the opcode-operand portion of the instruction specifies a given source or destination
register, that same register or portion of that register may be used as a source S1 and/or
S2 in the parallel data bus move operation. This allows data to be moved in the same
instruction in which it is being used as a source operand by a data ALU operation. That
is, duplicate sources are allowed within the same instruction. Note that S1 and S2
may specify the same register.
Class I Example:
:
ADDL B,A B,X1 Y:(R6)–N6,B ;2∗A+B ➞ A, update X1,B and R6
:
Explanation of the Class I Example: Prior to execution, the 56-bit B accumulator con-
tains the value $80:123456:789ABC, the 24-bit X1 register contains the value $000000,
the 16-bit R6 address register contains the value $2020, the 16-bit N6 address offset
register contains the value $0020 and the 24-bit Y memory location Y:$2020 contains the
value $654321. The execution of the parallel move portion of the instruction, B,X1
Y:(R6)–N6,B, moves the 24-bit limited negative saturation constant $800000 into the X1
register since the signed integer portion of the B accumulator was in use, uses the value
in the 16-bit R6 address register to move the 24-bit value in the Y memory location
Y:$2020 into the 56-bit B accumulator with automatic sign extension of the upper portion
of the accumulator (B2) and automatic zeroing of the lower portion of the accumulator
(B0), and finally uses the contents of the 16-bit N6 address offset register to update the
value in the 16-bit R6 address register. The contents of the N6 address offset register
are not affected.
R:Y Register and Y Memory Data Move R:Y
Before Execution After Execution
B B
$80:123456:789ABC $00:654321:000000
X1 X1
$000000 $800000
R6 R6
$2020 $2000
N6 N6
$0020 $0020
Y:$2020 Y:$2020
$654321 $654321