COP8SA-DM National Semiconductor, COP8SA-DM Datasheet - Page 23

• Manufacturer Part Number: COP8SA-DM
• Description: MODULE DEBUGGING FOR COP8SA
• Manufacturer: National Semiconductor

Specifications of COP8SA-DM

• Module/board Type: Debugger Module
• For Use With/related Products: Cop 8
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: *COP8SA-DM

data memory. The data pointer (PTR) is loaded with the address of a byte of data in
memory. To access the byte of data, the pointer can be used instead of using the address
itself (LD A, [PTR]). This is particularly useful when consecutive locations are accessed.
The data pointer can be incremented automatically after each access instead of
specifying the address each time.
Stack
The stack is a section of memory used to store data and address values. Stacks operate
in a LIFO (last in first out) manner. A stack pointer is used to address the stack. The
stack pointer is a register used to keep the address of the last piece of data put on the
stack. Usually the stack pointer is initialized to an address in memory. As data is put on
the stack, the stack pointer moves up or down in memory. The microcontroller uses the
stack to store return addresses during subroutine calls and interrupts. Some
microcontrollers also store status information on the stack before responding to
interrupts. The application program can use the stack to store data temporarily,
especially data to be passed between subroutines. Not all stacks are user accessible.
Examples:
Memory
Address
Register
1. Stack operation as a result of executing Jump-to-Subroutine (JSR), or PUSH
Stack Pointer
instructions.
Memory
Data
Figure 1-4 Separate Data and Code Space
Registers
CPU
Before
Empty
Empty
Empty
Stack
Internal Data Bus
Memory
Register
Data
A
Stack Pointer
MICROCONTROLLER BASICS
MUX
MUX
Return Address High
Return Address Low
Empty
Stack
After
ALU
1-11