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ELEN 33 Introduction to Digital Signal Processing Systems
Course Summary
31 May 2000
The processor is a circuit. It is controlled by stored instructions in memory. It performs a cycle
of fetching an instruction from memory using the program counter as the address and executing
the instruction.
Instructions:
The four components of an instruction are the label, mnemonic, operands, and comment.
Some instructions access and modify data.
 Load and store instructions move data between registers and memory. For the RISC
machine, which is a "load and store" machine, only these instructions can access
memory.
 Arithmetic and logic instructions perform operations on data such as addition and
subtraction, Boolean logic functions, and shifting. An ALU performs these
operations. The RISC machine performs these operations on registers only, but the TI
TMS320C31 can use operands from memory.
Some instructions change the flow of the program. Instructions are executed in the order
they are stored unless one of the following types of instructions is executed:
 Branch, jump and link, call, return
 These instructions may depend on condition codes set be arithmetic, logical, shift,
and load instructions.
The format of an instruction defines the meaning of each bit in the instruction word.
Instructions are executed by controlling the register output enables to control the input to
the ALU and controlling the write enables so that the result is stored in the correct
register.
Data Representations:
In order to interpret stored data, the set of values represented by the data must be known.
This is a data type. Bit patterns can represent integers, fixed point numbers, floating point
numbers, and ASCII character codes.
Arithmetic Operations:
 Integer addition of n-bit unsigned integers creates an overflow if the carry is set.
 Integer addition of n-bit signed integers in 2's complement form creates an overflow
if the carry into and out of the sign bit are different. This is equivalent to testing for
the wrong sign in the result.
 Addition of floating point numbers requires a normalization step.
 A barrel shifter implements shifts with logic.
 Multiplication of two n-bit integers produces a 2n bit result.
Copyright May 2000, Sally L. Wood
ELEN 033 Course Summary
Data Addressing Modes:
For immediate and direct addressing, the operand information is in the instruction. This
means that the operand information is known at the time of assembly.
 Immediate mode: the operand value is in the instruction.
 Direct Addressing mode: the operand address is in the instruction.
For register and indirect addressing, the operand information is in a register. Fewer
instruction bits are needed to specify operands when the operand information is in a
register rather than in the instruction.
 Register mode: the operand value is in a register.
 Indirect Addressing mode: the operand address is a register. Indirect addressing may
allow displacements and indexing.
Data Structures:
 Individual variables: usually accessed with direct addressing
 Arrays or lists: usually accessed with indirect addressing using a starting address and
a length.
 Stack: LIFO structure - contents of the stack are accessed using indirect addressing
through the "stackpointer". Status values are stackFull and stackEmpty.
 Queue: FIFO structure - contents of the queue are accessed using indirect addressing
through the "head" and the "tail" pointers. Memory implementation uses a circular
buffer. Status values are queueFull and queueEmpty
Program Structures:
If (expr) stmt1 else (stmt2);
While(expr) stmt;
For (expr1; expr2; expr3;) stmt;
Do stmt while(expr)
Test expr1
bne E
Instructions for stmt1
Br D
E: Instructions for stmt2
D: Continue
br T
W: Instructions for stmt
T: Test expr1
be W
Expr1;
While(expr2)
{
stmt;
expr3;
}
W: Instructions for stmt
T: Test expr1
be W
Bit testing with carry
Bit testing with indicator
bit
Use rotate or logical shift left
or right into the carry
position.
Check carry status
Note: If expr is always
true the program will loop
through the instructions
labeled with W forever.
Like the while loop except
the statement is always
executed once
Set testBit to 1
C: And testBit with word
of interest
bz to Z
Do "bit one" stuff
br S
Z: do "zero bit" stuff
S: Shift testBit left by one
br to C if not done
Copyright May 2000, Sally L. Wood
ELEN 033 Course Summary