+----------------------------------------------------------+
|                                                          |
| If the DSP56000 is given less than 64k words of external |
| RAM is there any reason to separate the P, X, and Y      |
| address spaces?  It seems to me that the best thing is to|
| overlay all three onto the same 64k address space. Will  |
| this introduce incompatibility with the DSP software     |
| available from Motorola?                                 |
|                                                          |
+----------------------------------------------------------+



Answer:                 
       The X/~Y, ~PS, and ~DS select lines can be used as additional
address lines since they have the same timing as A0-15. Thus one
physical memory, e.g., 8k x 24 can be partitioned  to support all
three memory spaces by appropriately encoding the select lines 
( see 2k, 2k, 4k  example below ). Such partitioning will be
transparent to the assembler and simulator.


            8k x 24 RAM
  
          +------------+
          |  $1FFF     |                         DSP56001
   4k --> |            |                      +------------+
          |  $1000     |                      |            |
          |------------|<---------------------| D0-23      |
          |  $0FFF     |                      |            |
   2k --> |            |                      |            |
          |  $0800     |                      |            |
          |------------|                      |            |
          |  $07FF     |                      |            |
   2k --> |            |                      |            |
          |     A0-13  |                      |            |
          |------------|                      |            |
                ^   ^                         |            |
                |   | 2      |----------|     |            |
                |   |--------| Encode   |<----|~PS         |
             12 |            | Logic    |<----|~DS         |
                |            |          |<----|X/~Y        |
                |            |----------|     |            |
                |                             |            |
                |-----------------------------|            |
                                              |------------|
