Destination - Source -->; Destination

Assembler Syntax:
SUBX -(Ax), -(Ay)

Attributes: Size = (Byte, Word, Long, Quad)

Description: Subtracts the source operand from the destination
operand and stores the result in the destination location.
The operands cas be addressed in two ways:
1. Data register to data register.
2. Memory to memory (Pre-decrement mode)
The size of the operation can be specified as byte, word, or

Condition Codes:
X Set the same as the carry bit.
N Set if the result is negative. Cleared otherwise.
Z Cleared if the result is nonzero. Unchanged otherwise.
V Set if an overflow is generated. Cleared otherwise.
C Set if a carry is generated. Cleared otherwise.

Note: Normally the Z condition code bit is set via programming before
the start of an operation. This allows successful tests for zero results
upon completion of multiple-precision operations.