Lec. 10 Assembly Programming Dr. Tamer Samy Gaafar Microprocessors

Quiz Draw a flow chart for converting an octal number to binary. Write the required program assuming the octal number is 356 where address 56 …………. Contains 3 address 57 …………. Contains 5 address 58 …………. Contains 6 Store the result at address 59.

The 6800 Microprocessor

6800 Microprocessor It was first released by Motorola in the mid 1970’s. Today, it is being second sourced by several other companies is another version of this proc. The primary difference between 6800 & 6808 is the means by which clock signals are generated. The 6808 has an on-chip clock circuit.

6800 Microprocessor

Architecture of 6800 Microprocessor Computer Architecture : is used to describe the construction of computer i.e. Register Size and arrangement. Bus Configuration

The Programming Model

The Programming Model of 6800 MPU

Two Accumulators Accumulator A (ACCA) Accumulator B (ACCB)

Program Counter PC …………… 16 bits. Address is 16 bits …… address. How can we specify a 16 bit address with an 8-bit address bus? Extended addressing mode ….two bytes are used to represent each address.

Condition Code Register

Index Register 16 bit general purpose register. It allows a powerful addressing mode called indexed addressing. It holds 2 byte instead of one byte.

Block Diagram of the 6800 MPU

Note Address bus is 16 bit. Address registers are 16 bits. Any of the 16 bit registers can be loaded from data bus which is only 8 bits. So 2 operations are required. Upper half of the affected register is loaded first then the lower half.

Instruction Set of The 6800 MPU

Types of Instructions Arithmetic Data Handling. Logic. Data Test. Index Register. Stack Pointer. Jump, Branch & Condition Code.

Arithmetic Instructions

means condition code is un affected. means test and set if true, clear otherwise.

Data Handling Instructions

Rotate Left

Rotate Right

Arithmetic Shift Left

Arithmetic Shift Right

Logical Shift Right

TAB & TBA Instruction TAB Copies contents of accumulator A into accumulator B. TBA Copies contents of accumulator A into accumulator B.

Logical Instructions

Data Test Instructions

The End