#1 register contents can't be written to odd addresses.

[Rogan Creswick]

When the machine stores a value from a register to an
address with an odd
value,
it actually stores the value to the next lower
even-numbered address. For
example, storing two bytes from register C to address
45 actually puts the
bytes at address 44.

When the machine stores a value from a register to an
even-numbered address,
it zeroes out the value in the next higher odd-numbered
address. For
example,
storing two bytes from register C to address 00 causes
the contents of 01 to
be zeroed out.