Java virtual Machine implementation iadd microcommand improvization -

wanna ask question of our computer structure exam here sure. below add command of mic-1 ijvm. asked write new iaddtriple command add 3 top words of stack , store on stack again.

iadd1 mar = sp = sp − 1; rd read in next-to-top word on stack iadd2 h = tos h = top of stack iadd3 mdr = tos = mdr + h;wr;go main1 add 2 top words, write top of stack 

my answer ;

iaddtriple1 mar = sp = sp − 1; rd  iaddtriple2 h = tos h =  iaddtriple3 h = mdr = tos = mdr + h  iaddtriple4 mar = sp = sp − 1; iaddtriple5 mdr = tos = mdr + h ; wr;go main1 

i want ask if iaddtriple3 step legal. 1 of friends told me h=blabla +h assignment should illegal shouldn't used. time diagram of data path cycle proves me right. in advance.

iaddtriple3  h = mdr = tos = mdr + h  

it possible perform

h = h + mdr 

since h can specified in c-bus bits, alu operation + b, b register mdr. actual microinstruction

0003c8000 

the first 2 hex digits numbers, third hex digit 0 or 8.