Motorola 6800

Motorola 6800 Microprocessor

The 6800 is a microprocessor produced by Motorola and released shortly after the Intel 8080 in 1975. It had 78 instructions, including the (in)famous, undocumented Halt and Catch Fire (HCF) bus test instruction. It may have been the first Microprocessor with an index register.

It was usually packaged in a 40 pin DIP (dual-inline package).

Several first-generation microcomputers of the 1970s, available by mail order as kits or in assembled form, used the 6800 as their CPU; examples are the MEK6800D2 development board, the SWTPC 6800 (the first computer to use the 6800), the MITS Altair 680 range (MITS offered these as alternatives to its Altair 8800 which used the Intel 8080), several of the Ohio Scientific designs, Gimix, Smoke Signal Broadcasting, Midwest Scientific, and the Newbear 77/68.

The 6800 'fathered' several descendants, the pinnacle being the greatly extended and semi-compatible 6809, which was used in the Vectrex video game console and the TRS-80 Color Computer, among several others. There are also many microcontrollers descended from the 6800 architecture, such as the Motorola 6801/6803, 6805, 68HC08, 68HC11 and 68HC12.

Hitachi, Ltd. acted as a second source for many of Motorola's CPUs, and also produced its own derivatives including the 6301 and 6303, which could run 6800 code. These microprocessors also had a couple of extra instructions added to their instruction sets.

Competitor MOS Technology came up with an architectural relative of the 6800, with its 6502 ('lawsuit compatible' MPU) and its successors. The 6502 did not have the 16 bit registers of the 6800, but had more addressing modes. The 6502 was used in many computers and game consoles during the late 1970s and early-to-mid-1980s (most notably the Atari 2600, Apple II, the Commodore PET, VIC-20 and Commodore 64, and the Acorn Electron/BBC Microcomputer), and the Nintendo Entertainment System or NES.

Program model

7 A 0

7 B 0

15 X 0

15 PC 0

15 SP 0

7 CCR 0

2*8 bits

16 bits

16 bits

16 bits

8 bits

A - Accumulator A
B - Accumulator B
X - Index register
PC - Program Counter
SP - Stack Pointer
CCR - Conditional Code Register

See also

• Motorola 68000

External links

• 680x images and descriptions at cpu-collection.de
• Instruction set summary
• Java Applet Simulator of a simplified M6800 Microprocessor

This article is based on material taken from the Free On-line Dictionary of Computing prior to 1 November 2008 and incorporated under the "relicensing" terms of the GFDL, version 1.3 or later.