[Z] ← ¬(<bit number> OF [destination])
<bit number> OF [destination] ← 0
BCLR Dn,<ea>
BCLR #<data>,<ea>Size byte, longword
A bit in the destination operand is tested and the state of the specified bit is reflected in the condition of the Z-bit in the condition code. After the test, the state of the specified bit is cleared in the destination. If a data register is the destination, the bit numbering is modulo 32, allowing bit manipulation of all bits in a data register. If a memory location is the destination, a byte is read from that location, the bit operation performed using the bit number modulo 8, and the byte written back to the location. Bit zero refers to the least-significant bit. The bit number for this operation may be specified either by an immediate value or dynamically by the contents of a data register.
If the operation BCLR #4,$1234 is carried out and the contents of memory location $1234 are 11110102, bit 4 is tested. It is a 1 and therefore the Z-bit of the CCR is set to 0. Bit 4 of the destination operand is cleared and the new contents of $1234 are: 111010102.
| X | N | Z | V | C |
|---|---|---|---|---|
| - | - | * | - | - |
Z: set if the bit tested is zero, cleared otherwise.
| Dn | An | (An) | (An)+ | ‑(An) | (d,An) | (d,An,Xi) | ABS.W | ABS.L | (d,PC) | (d,PC,Xn) | imm |
|---|---|---|---|---|---|---|---|---|---|---|---|
| ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ |
Note that data register direct (i.e., Dn) addressing uses a longword operand, while all other modes use a byte operand.
From MOTOROLA M68000 FAMILY Programmer's reference manual. Copyright 1992 by Motorola Inc./NXP. Adapted with permission.