Digital Electronics: Principles, Devices and Applications

Microprocessors 549memory by using its memory management system. The 80286 is packaged in a 68-pin ceramic flatpackage and PGA, CLCC and PLCC packages. The 80286 microprocessor can work at a maximumfrequency of 12.5 MHz.13.10.4 MC68000 Microprocessor68000 is the first member of Motorola’s family of 16-bit and 32-bit processors. It is a successor tothe 6809 and was followed by the 68010. The 68000 has 32-bit registers but only a 16-bit ALU andexternal 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 busin 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-pinceramic DIP and the 68-pin ceramic LLCC package. Figure 13.16 shows a simplified block diagramof the 68000 microprocessor.13.10.4.1 68000 registersThe 68000 microprocessor has 16 32-bit registers and a 32-bit program counter. There are eight dataregisters for byte (eight-bit), word (16-bit) and long-word (32-bit) operations. There are seven addressregisters. These seven registers and the user stack pointer (USP) may be used as software stack pointersand base address registers. They are also used for word and long-word operations. Data, address andUSP registers may also be used as index registers. In supervisor mode, the upper byte of the statusregister and the supervisor stack pointer (SSP) are also available to the programmer. The status registercontains 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 insupervisor (S) mode.13.10.4.2 Instruction Set68000 has the following instruction types: data movement operations, integer arithmetic operations,logical operations, shift and rotate operations, bit manipulation operations, program control operationsand system control operations.13.10.4.3 Addressing ModesThe 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 registerindirect, register indirect with offset, indexed register indirect with offset).