Unused I/Os for Dual port SRAM's

Question: - What should I do with the unused I/O pins? - Can unused I/Os be tied to each other if the relevent byte enable is disabled? - What should I do if my processor is only 32 bits wide and the data bus is 36 bits wide?

 

Answer:

Not all data I/Os have to be used. If the interface to one of our dual-ports does not exactly match, then  the unused data I/Os need to be pulled high or low. This is because it is never safe to leave an input floating.

If an entire byte (9 bits) is not used and there is a shared byte enable, then the unused outputs can be tied to each other if the relevant byte enable is not enabled during a read operation. The only recommendation would be to tie them to a known state.

The reason our memory arrays do not seem to match perfectly with standard interfaces (36 vs. 32 bits) is that we allow extra bits for customer use such as parity check. Usually, it is as simple as using only the MSB or LSB to align the interfaces and tying the unused bits high or low. However, if the interface is using byte enables similar to the function of the B0#-B3# pins of the dual-port, it may be better to map each byte together, leaving 1 in each section free. For example:

                                                                                                           
   

     CONNECTIONS

  
   

     Tied to VCC/GND

  
   

     x32 PROCESSOR

  
   

     x36 DUAL-PORT

  
     
   

     D0-D7

  
   

     D0-D7

  
   

     D8

  
   

     D8-D15

  
   

     D9-D16

  
   

     D17

  
   

     D16-D23

  
   

     D18-D25

  
   

     D26

  
   

     D24-D31

  
   

     D27-D34

  
   

     D35