Motorola DSP96002 - Manual (Page 85)

MOTOROLA DSP96002 USER’S MANUAL 6 - 9
6.4.2 Memory Access Processing
One or more of the DSP96002 memory sources (X data memory, Y data memory and program memory)
may be accessed during the execution of an instruction. Each of these memory sources may be internal or
external to the DSP96002. Three address buses (XAB, YAB and PAB) and four data buses (XDB, YDB,
PDB and GDB) are available for internal memory core (as opposed to DMA) accesses during one instruc-
tion cycle.
The DSP96002 has two external expansion ports (Port A and Port B), that function as extensions of the
internal address and data buses for external memory accesses. If all memory sources are internal to the
DSP96002, one or more of the three memory sources may be accessed in one instruction cycle (i.e., pro-
gram memory access or program memory access plus an X, Y, XY or L memory reference; refer to Section
5.6 for a description of operand references). However, when one or more of the memories are external to
the DSP96002, and the external memories are located in the same expansion port, memory references
may require additional instruction cycles.
If, in one instruction cycle, more than one external access is required on the same port, the accesses will
be made with the following priority:
1. X memory.
2. Y memory.
3. Program memory.
4. DMA.