|   4 LSB      
                  +<--------> PC 
                  |              
                  |              
       4 LSB      |              
MAR  <------------+<--------> A  
 |                |           |  
 | 4 LSB          |           |  
 |                |           |  
 v                |           v  
RAM <------------>|<-------- ALU 
                  |           ^  
                  |           |  
                  |           |  
                  |           |  
    <-------------+           |  
 IR ------------->|<--------> B  
 |    4 LSB       |              
 |                |              
 |                |              
 | 4 MSB          +---------> OUT
 |                |            | 
 v                |            | 
 ins                           v 
 decoder                   DISPLAY