Microprocessors
545
Output
Buffers
A15 A14 A13 A12 A11 A10 A9 A8
Program
Counter L
Stack
Pointer L
Index
Register L
Accumulator
A
Accumulator
B
Condition
Code Register
ALU
Program
Counter H
Stack
Pointer H
Index
Register H
Instruction
Decode
And
Control
Instruction
Register
Data Buffer
RESET
NMI
HALT
Interrupt Request
Extal
Three state control
Bus Available
Valid Memory Address
Read/Write, R/W
Output
Buffers
D7 D6 D5 D4 D3 D2 D1 D0
A7 A6 A5 A4 A3 A2 A1 A0
φ1
φ2
Figure 13.13 Block diagram of 6800.
13.9.2.1 6800 Registers
The 6800 microprocessors have six internal registers, namely accumulator A (ACCA), accumulator B
(ACCB), an index (IX), a program counter, a stack pointer (SP) and a condition code register.
13.9.2.2 Addressing Modes
It has the implied addressing mode, accumulator addressing mode, immediate addressing mode, direct
addressing mode, extended addressing mode, relative addressing mode and indexed addressing mode.
13.9.2.3 Instruction Set
The 6800 instruction set consists of 72 instructions. It supports data moving instructions, arithmetic
instructions (add, subtract, negate, increment, decrement and compare), logic instructions (AND,