Abstract
The 8-bit microprocessor has not been rendered obsolete by newer and more powerful 16- and 32-bit microprocessors. Many applications are more than adequately served by 8-bit microprocessors, with their lower-cost address and data buses. However, there is a ‘grey area’ in which 8-bit chips are not sufficient but 16-bit chips represent an uneconomic ‘overkill’. A significant limitation of 8-bit microprocessors with 16-bit address buses is their inability to access more than 64 kbyte of data. This application shows how the SN54/74LS610-3 series of memory mapping units enables an 8-bit microprocessor to access memories much larger than 64 kbyte without significantly increasing the chip count of the system. Note that a memory mapping unit cannot simply be engineered into a microprocessor system without adding the appropriate software, as the 8-bit microprocessor can still address only 64 kbyte of logical address space at any instant. Software is usually included in the operating system to map 64 kbyte of the physical memory onto the logical address space.
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