OVERVIEW5 - 4 PROGRAM CONTROL UNIT
MOTOROLA
All of the PCU registers are read/write to facilitate system debugging. Although none ofthe registers are 24 bits, they are read or written over 24-bit buses. When they are read,the least significant bits (LSBs) are significant, and the most significant bits (MSBs) arezeroed as appropriate. When they are written, only the appropriate LSBs are significant,and the MSBs are written as don’t care.
CLOCK
GENERATOR
PERIPHERAL
PINS
INTERNAL
DATA
BUS
SWITCH
PROGRAM
RAM/ROM
EXPANSION
PROGRAM
INTERRUPT
CONTROLLER
PROGRAM
DECODE
CONTROLLER
PROGRAM
ADDRESS
GENERATOR
YAB
XAB
PAB
YDB
XDB
PDB
GDB
MODC/NMI
MODB/IRQB
RESET
DATA ALU
24X24+56→56-BIT MAC
TWO 56-BIT ACCUMULATORS
EXTERNAL
ADDRESS
BUS
SWITCH
BUS
CONTROL
EXTERNAL
DATA BU S
SWITCH
ADDRESS
DATA
16 BITS
24 BITS
PORT A
MODA/IRQA
PLL
X MEMORY
RAM/ROM
EXPANSION
Y MEMORY
RAM/ROM
EXPANSION
ADDRESS
GENERATION
UNIT
OnCE™
PERIPHERAL
MODULES
EXPANSION
AREA
CONTROL

24-Bit

56K Mod-

Figure 5-2 DSP56K Block Diagram
Program Control Unit