COP8SA-DM National Semiconductor, COP8SA-DM Datasheet - Page 25

• 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

Accumulator vs Register
An accumulator-based microcontroller operates in a manner different from a register-
based microcontroller. The difference is due to the different ALU architectures. The most
common are:
Another difference is due to the difference between the microcontroller architectures in
terms of where numbers must be located in order for them to be operated on by the ALU
of the microcontrollers.
Example: Adding two numbers
Adding two numbers in an accumulator-based machine requires that one of the numbers
be located in the accumulator and the other one in data memory. The result of the
addition is placed back in the accumulator.
A register-based machine does not require that any of the addends be in the accumulator.
Instead, the two numbers may be in registers in memory. The result may be specified to
be placed in one of the registers being used in the addition, a third register, or the
accumulator.
What's the difference? Is one method better than another?
Accumulator based machines require one of the operands to be located in the
Accumulator. Therefore, only one operand location must be specified in instructions.
Register based machines do not require the operands to be in a particular location.
Therefore, the location of both operands must be specified in instructions.
The decoding of register-based instructions and the fetching of operands generally
requires more time than would be required to execute an accumulator-based instruction.
5. Timer run, which tells microcontroller to start the timer.
1. Stack based: a no address machine
2. Accumulator based: a one-address machine
3. Register based: a two- or three-address machine
Figure 1-5 Adding Two Numbers Using Accumulator Based Machine
Addend #1
Memory
Data
Addend #2
Accumulator
Memory Data
Register
MICROCONTROLLER BASICS
ALU
1-13