Microprocessors
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memory by using its memory management system. The 80286 is packaged in a 68-pin ceramic flat
package and PGA, CLCC and PLCC packages. The 80286 microprocessor can work at a maximum
frequency of 12.5 MHz.
13.10.4 MC68000 Microprocessor
68000 is the first member of Motorola’s family of 16-bit and 32-bit processors. It is a successor to
the 6809 and was followed by the 68010. The 68000 has 32-bit registers but only a 16-bit ALU and
external data bus. It has 24-bit addressing and a linear address space. Addresses are computed as 32-bit,
but the top eight bits are cut to fit the address bus into a 64-pin package (address and data share a bus
in the 40-pin packages of the 8086). It is available in several clock frequencies. These include 6, 8, 10,
12.5, 16.67 and 25 MHz. The 68000 microprocessor is available in two packages, namely the 64-pin
ceramic DIP and the 68-pin ceramic LLCC package. Figure 13.16 shows a simplified block diagram
of the 68000 microprocessor.
13.10.4.1 68000 registers
The 68000 microprocessor has 16 32-bit registers and a 32-bit program counter. There are eight data
registers for byte (eight-bit), word (16-bit) and long-word (32-bit) operations. There are seven address
registers. These seven registers and the user stack pointer (USP) may be used as software stack pointers
and base address registers. They are also used for word and long-word operations. Data, address and
USP registers may also be used as index registers. In supervisor mode, the upper byte of the status
register and the supervisor stack pointer (SSP) are also available to the programmer. The status register
contains the interrupt mask as well as the condition codes [extend (X), negative (N), zero (Z), overflow
(V) and carry (C)]. It also has status bits to indicate whether the processor is in trace (T) mode or in
supervisor (S) mode.
13.10.4.2 Instruction Set
68000 has the following instruction types: data movement operations, integer arithmetic operations,
logical operations, shift and rotate operations, bit manipulation operations, program control operations
and system control operations.
13.10.4.3 Addressing Modes
The 68000 microprocessor supports the following addressing modes:
1. Register direct addressing (data register direct and address register direct).
2. Absolute data addressing (absolute short and absolute long).
3. Program counter relative addressing (relative with offset, relative with index and offset).
4. Register indirect addressing (register indirect, post-increment register indirect, predecrement register
indirect, register indirect with offset, indexed register indirect with offset).
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memory by using its memory management system. The 80286 is packaged in a 68-pin ceramic flat
package and PGA, CLCC and PLCC packages. The 80286 microprocessor can work at a maximum
frequency of 12.5 MHz.
13.10.4 MC68000 Microprocessor
68000 is the first member of Motorola’s family of 16-bit and 32-bit processors. It is a successor to
the 6809 and was followed by the 68010. The 68000 has 32-bit registers but only a 16-bit ALU and
external data bus. It has 24-bit addressing and a linear address space. Addresses are computed as 32-bit,
but the top eight bits are cut to fit the address bus into a 64-pin package (address and data share a bus
in the 40-pin packages of the 8086). It is available in several clock frequencies. These include 6, 8, 10,
12.5, 16.67 and 25 MHz. The 68000 microprocessor is available in two packages, namely the 64-pin
ceramic DIP and the 68-pin ceramic LLCC package. Figure 13.16 shows a simplified block diagram
of the 68000 microprocessor.
13.10.4.1 68000 registers
The 68000 microprocessor has 16 32-bit registers and a 32-bit program counter. There are eight data
registers for byte (eight-bit), word (16-bit) and long-word (32-bit) operations. There are seven address
registers. These seven registers and the user stack pointer (USP) may be used as software stack pointers
and base address registers. They are also used for word and long-word operations. Data, address and
USP registers may also be used as index registers. In supervisor mode, the upper byte of the status
register and the supervisor stack pointer (SSP) are also available to the programmer. The status register
contains the interrupt mask as well as the condition codes [extend (X), negative (N), zero (Z), overflow
(V) and carry (C)]. It also has status bits to indicate whether the processor is in trace (T) mode or in
supervisor (S) mode.
13.10.4.2 Instruction Set
68000 has the following instruction types: data movement operations, integer arithmetic operations,
logical operations, shift and rotate operations, bit manipulation operations, program control operations
and system control operations.
13.10.4.3 Addressing Modes
The 68000 microprocessor supports the following addressing modes:
1. Register direct addressing (data register direct and address register direct).
2. Absolute data addressing (absolute short and absolute long).
3. Program counter relative addressing (relative with offset, relative with index and offset).
4. Register indirect addressing (register indirect, post-increment register indirect, predecrement register
indirect, register indirect with offset, indexed register indirect with offset).