Destination Sign-Extended -->; Destination
extends byte to word
extends word to long word
Attributes: Size = (Word, Long)
Description: Extends a byte in a data register to a word or a
word in a data register to a long word, by replicating the
sign bit to the left. If the operation extends a byte to a word,
bit  of the designated data register is copied to bits [15:8]
of that data register. If the operation exntends a word to a
long word, bit  of the designated data register is copied
to bits [31:16] of the data register.
X Not affected.
N Set if the result is negative. Cleared otherwise.
Z Set if the result is zero. Cleared otherwise.
V Always cleared.
C Always cleared.