mdr.vhd
 	This code contains the data memory interface and the associated registers 
 like the LMDR, SMDR and the DMAR
 LMDRbus 	
 Output of the LMDR(Load Memory Data Register) and input
                 to the LMDR Zero detector
 LMDR_Select 
 LMDR select line which selects whether the value in
		  the databus be sign/zero extended or simply passed to the
		  LMDR register
 LMDR_Zflag	
 Indicates whether the LMDR register contains a Zero
 DMemRead	
 Load signal of the LMDR
 SMDRload 	
 Load enable signal of the SMDR
 SMDR_Select	
 Select line of the SMDR multilplexer that selects among the
   		   Bregout, Destbus_a, Dsetbus_b and the LMDRbus. Output of 
		   the MUX is fed to the SMDR
 Databus	
 Output of the SMDR
 Destbus_a	
 Previous value of the Destination bus
 Destbus_b    
 Second previous value of the destination bus
 Bregout	
 Output of the B register in the register file block
 DMARload	
 Load line of the DMAR
 Daddrbus 	
 Output of the DMAR
 Destbus 	
 Input to the DMAR