55
The 68000's Instruction Set
The only legal addressing modes are data register direct and
memory to memory with address register indirect using auto-
decrementing.
Condition codes:
X N Z V C
* * * * *
Z: Cleared if the result is non-zero, unchanged otherwise. The Z-
bit can be used to test for zero after a chain of multiple precision
operations.
SWAP
Swap register halves
Operation:
[Register(16:31)]
←
[Register(0:15)];
[Register(0:15)]
←
[Register(16:31]
Syntax:
SWAP Dn
Attributes:
Size = word
Description:
Exchange the upper and lower 16-bit words of a data register.
Application:
The
SWAP
Dn
instruction enables the higher-order word in a register
to take part in word operations by moving it into the lower-order
position.
SWAP
Dn
is effectively equivalent to
ROR.L
Di,Dn
, where
[Di] = 16. However,
SWAP
clears the C-bit of the CCR, whereas
ROR
sets it according to the last bit to be shifted into the carry bit.
Condition codes:
X N Z V C
- * * 0 0
The N-bit is set if most-significant bit of the 32-bit result is set
and cleared otherwise. The Z-bit is set if 32-bit result is zero and
cleared otherwise.
TAS
Test and set an operand
Operation:
[CCR]
←
tested([operand]); [destination(7)]
←
1
Syntax:
TAS <ea>
Attributes:
Size = byte
Description:
Test and set the byte operand addressed by the effective address
field. The N- and Z-bits of the CCR are updated accordingly. The
Summary of Contents for 68000
Page 1: ...Motorola 68000 s Instruction Set ...
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