next up previous contents index

[ENGN3213 Home]

Bus Sizing

  The 68000 has a 16 bit data bus. This means that the processor can transfer 16 data bits in parallel. In this sense it is a 16 bit processor. It has a 23 bit address bus (externally), and so it can address 223 16-bit address locations, or 224 8-bit locations. Internaly, the 68000 has a 32 bit architecture. Each address location is 1 byte in size, i.e. 8 bits.

A word is 16 bits, and a longword is 32 bits.      

As we will see, it is important to understand how bytes, words, and longwords are used and stored in memory.

The 5206, in contrast, is a 32 bit machine, with a 32 bit data bus. It has internally a 32 bit address bus with a 28 bit external address bus.

Memory length is often given as a multiple of 1,024 = 210 locations, abbreviated 1K. Thus 16 address lines corresponds to 64K bytes (64KB) of memory, or 65,536 bytes. 1MB is 1,048,576 bytes.


next up previous contents index

[ENGN3213 Home]

ANU Engineering - ENGN3213