CLeaR
NAME
CLR -- Clear
SYNOPSIS
CLR <ea>
Size = (Byte, Word, Long)
FUNCTION
Clears the destination operand to zero.
On an MC68000 and MC68HC000, a CLR instruction does both a
read and a write to the destination. Because of this, this
instruction should never be used on custom chip registers.
FORMAT
-----------------------------------------------------------------
|15 |14 |13 |12 |11 |10 | 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
|---|---|---|---|---|---|---|---|-------|-----------|-----------|
| 0 | 1 | 0 | 0 | 0 | 0 | 1 | 0 | SIZE | MODE | REGISTER |
----------------------------------------=========================
<ea>
REGISTER
<ea> specifies destination operand, addressing modes allowed are:
--------------------------------- -------------------------------
|Addressing Mode|Mode| Register | |Addressing Mode|Mode|Register|
|-------------------------------| |-----------------------------|
| Dn |000 |N° reg. Dn| | Abs.W |111 | 000 |
|-------------------------------| |-----------------------------|
| An | - | - | | Abs.L |111 | 001 |
|-------------------------------| |-----------------------------|
| (An) |010 |N° reg. An| | (d16,PC) | - | - |
|-------------------------------| |-----------------------------|
| (An)+ |011 |N° reg. An| | (d8,PC,Xi) | - | - |
|-------------------------------| |-----------------------------|
| -(An) |100 |N° reg. An| | (bd,PC,Xi) | - | - |
|-------------------------------| |-----------------------------|
| (d16,An) |101 |N° reg. An| |([bd,PC,Xi],od)| - | - |
|-------------------------------| |-----------------------------|
| (d8,An,Xi) |110 |N° reg. An| |([bd,PC],Xi,od)| - | - |
|-------------------------------| |-----------------------------|
| (bd,An,Xi) |110 |N° reg. An| | #data | - | - |
|-------------------------------| -------------------------------
|([bd,An,Xi]od) |110 |N° reg. An|
|-------------------------------|
|([bd,An],Xi,od)|110 |N° reg. An|
---------------------------------
SIZE
00->one Byte operation
01->one Word operation
10->one Long operation
RESULT
X - Not affected
N - Always cleared
Z - Always set
V - Always cleared
C - Always cleared
SEE ALSO
MOVE MOVEQ
BCLR BFCLR
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& witbrock@cs.cmu.edu