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MOVH : MOVe Halfword High
This instruction overwrites the high halfword of a register.
Like MOV, this instruction copies the lower part to the destination
but the higher bits come from either
 -  a register's content (si4)
       (short register form that writes to snd,
        or extended register form that writes to dst3)
 
-  a 4-bit immediate value (si4)
      (short immediate form that writes to snd,
       or extended immediate form that writes to dst3)
 
-  a 16-bit value
       (long immediate form with YASEP16 that writes to si4)
This instruction is created to create 32-bits data in YASEP32 with code sequences such as:; put 12345678h in R1
 MOV  5678h R1 ; first, write the LSB
 MOVH 1234h R1 ; then overwrite the MSB