Programming Model; Section 5.4 Programming Model; Program Counter - Motorola DSP56000 Manual

24-bit digital signal processor
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23 16 15
*
LOOP ADDRESS
REGISTER (LA)
23 16 15
*
PROGRAM
COUNTER (PC)
31
SSH
Figure 5-4 Program Control Unit Programming Model
ation, move the contents in accumulator A into the location in Y data memory pointed to
by R4 and postdecrement R4. The third instruction, I3, is the same as I1, except the
rounding operation is not performed.
5.4

PROGRAMMING MODEL

The program control unit features LA and LC registers which support the DO loop instruc-
tion and the standard program flow-control resources, such as a PC, complete SR, and
SS. With the exception of the PC, all registers are read/write to facilitate system debug-
ging. Figure 5-4 shows the program control unit programming model with the six registers
and SS. The following paragraphs give a detailed description of each register.

5.4.1 Program Counter

This 16-bit register contains the address of the next location to be fetched from program
memory space. The PC can point to instructions, data operands, or addresses of oper-
ands. References to this register are always inherent and are implied by most instructions.
5 - 8
PROGRAMMING MODEL
PROGRAM CONTROL UNIT
0
23 16 15
*
LOOP COUNTER (LC)
0
23 16 15
8 7
MR
CCR
*
STATUS
REGISTER (SR)
16 15
SSL
0
SYSTEM STACK
PROGRAM CONTROL UNIT
0
0
23
8 7
*
OPERATING MODE REGISTER (OMR)
23
6 5
1
*
STACK POINTER (SP)
*
READ AS ZERO, SHOULD BE WRITTEN
WITH ZERO FOR FUTURE COMPATIBILITY
15
6
5
4
3
2
1
0
*
DE MB
MA
SD
*
MC
YD
0
MOTOROLA

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