TMS320F datasheet(69/389 Pages) TI

69 / 389 page

Program-Address Generation

5-5

Program Control

plete, a return instruction transfers the return address from the top of the stack

to the program counter.

When the eight levels are not used for return addresses, the stack may be used

for saving context data during a subroutine or interrupt service routine or for

other storage purposes.

You can access the stack with two sets of instructions:

- PUSH and POP. The PUSH instruction copies the 16 LSBs of the accumu-

lator to the top of the stack. The POP instruction copies the value on the

top of the stack to the 16 LSBs of the accumulator.

- PSHD and POPD. These instructions allow you to build a stack in data

memory for the nesting of subroutines or interrupts beyond eight levels.

The PSHD instruction pushes a data-memory value onto the top of the

stack. The POPD instruction pops a value from the top of the stack to data

memory.

Whenever a value is pushed onto the top of the stack (by an instruction or by

the address-generation logic), the content of each level is pushed down one

level, and the bottom (eighth) location of the stack is lost. Therefore, data is

lost (stack overflow occurs) if more than eight successive pushes occur before

a pop. Figure 5–2 shows a push operation.

Figure 5–2. A Push Operation

Before Instruction

After Instruction

Accumulator

or memory

location

Stack

12h

86h

12h

54h

86h

3Fh

54h

TMS320F 데이터시트(PDF) 69 Page - Texas Instruments