Motorola 68000

by

Matt Bachiochi, Will Lowrey, Matt Petrick, Scott Schenkein, and Mark Wade

Registers

• About

• Status Bits

• Distribution

Registers: About

• General purpose register-based machine

• Every data register can be used as an accumulator or a temp register

• Data bytes are arranged with least-significant byte at the higher address

• This is known as the endian approach

Registers: Status Bits

• The M68000 has 10 status bits– T: Trace bit 15

– S: Supervisor Mode bit 13

– I2: Interrupt Mask 2 bit 10

– I1: Interrupt Mask 1 bit 9

– I0: Interrupt Mask 0 bit 8

– X: Sign Extend bit 4

– N: Negative bit 3

– Z: Zero bit 2

– V: Overflow bit 1

– C: Carry bit 0

Registers: Distribution

• Total number of registers is 19– 8 are general data– 7 are general address– 2 are stack pointers– 1 processor status word– 1 program counter

Addressing Modes

• The Motorola 68000 has 14 different addressing modes– Register Direct– Address Register Indirect– Absolute Data Register– Program Counter Relative– Immediate Data– Implied Addressing

Technology

• The 68000 was originally a 5 volt NMOS

dynamic construction

• Later updated to a CMOS

• CMOS-TTL bridged busses

• Bus Arbitration Control circuitry

Motorola 68000

Is a CISC!

With only one data pipe.

Speed

• Clock speed: 8 - 16 Mhz

• Dhrystones: – Raw processing benchmarks integer data– 2100 - 4376

• MIPS: – Millions of instructions per second– 1.2 - 2.5

The Motorola 68000 Processor

Historical Computers

The Apple LISA (1983)

• The Precursor to the Macintosh

• Local Integrated Software Architecture

• 1 Meg Ram, 10 Meg HDD

• Cost: $10,000

The Apple Macintosh (1984)

• Known as the “Mac-in-the-box”

• First to use MacOS• Had 128K RAM• No hard drive• Cost: $2500• Market for Radiation

Underwear

The Commodore Amiga (1985)

• The fastest commercial M68000

• Had 512K RAM• Capable of Color• Cost: $2,800