LH是格式。指令格式：Lh Rt,I(Rs) Rt <- M(Rs+I)。
Lh--load half word
指令格式：Lh Rt,I(Rs) Rt <- M(Rs+I)
sign extended immidiate. Two bytes from storage is
loaded into the 2 less significant bytes of Rt.
The sign of these 2 bytes is extended on the 2 most
significant bytes.