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In the memory map we usually can find three pieces of information for each type of memory: the starting address, the memory size, and the ending address. In fact, given any two of these three, one can calculate the third. Let us continue to use the memory map defined on the previous pages as an example. To design a memory system, it is easier to use binary numbers to represent the starting address and ending address for each chip. By comparing the starting address and ending address of each type of memory and considering all the memory addresses between the starting and ending addresses one can find that (1) certain bits of the memory address do not change for each memory chip and (2) certain bits of memory addresses change between 0 and 1 for a particular chip. The bits that change for each memory chip are underlined.
If you count the number of address bits that changes for the chip, you find that this number matches the number of address pins of the memory chip. Therefore, these address lines are directly connected to the memory address pins as shown on the next page. For example, the EEPROM chip has 10 address pins and the changing bits for EEPROM are 10. Therefore, the changing bits are directly connected to the address pins of the chip.