The Motorola 68000 microprocessor is Motorola’s first 16-bit microprocessor. The 68000 is not program compatible with Motorola’s family of 8-bit microprocessors. For the designing of instruction set the Motorola has given more trace on its powerfulness and simplicity rather than compatibility. The Motorola 68000 Features are
1.It is a 16-bit microprocessor.
2.There are seventeen 32-bit data and address registers, a 32-bit Program Counter (of which only 24 bits are used) and a 16-bit status register.
3.The data registers can be used to handle 8-bit bytes, 16-bit words, or 32-bit long words.
4.There are seven general purpose address registers (A0-A6). These registers can handle either 16-bit word or 32-bit word or 32-bit long word operands.
5.The 68000 supports pipelining.
6.The 68000 does not attempt to accommodate different complexities of system configurations such as dual function pins in 8086 and different versions in The 68000 provides separate pins for every data line and address output line. This is possible since the 68000 is contained in a 64-pin package and as a result there is no shortage of pin connections.
7.The 68000 has built-in logic to handle bus access arbitration in multi CPU configuration.
8.The 68000 can directly access upto 16 Mbytes of memory with its 24-bit address The. memory space may, be expanded to 64 Mbytes by using the function code lines.
9.In order to implement operating systems and protection features, the 68000 can be operated in two modes.
1) Supervisor mode
2) User mode.
Supervisor and User modes also have separate stack pointers. Thus, in program-intensive applications, systems software (executed in Supervisor Mode) can be separated from applications programs (executed in User mode).
10.The 68000 provides 56 basic instructions with 14 addressing modes, and 5 data The 68000 includes more than 1000 opcodes. The fastest instruction is MOVE register, register and is executed in 500 ns at 8MHz chick. The slowest instruction is 32-bit by 16-bit divide, which is executed in 21.25 μs at 8MHz clock.
11.Like the 8-bit Motorola microprocessors, the 68000 supports memory mapped I/O. Thus, the 68000 instruction set does not include any IN or OUT instruction.