Monday, May 4, 2015

4x4 Full-Adder EEPROM Lookup Table

My first use for the EEPROM programmer I have been working on is a lookup table. This will be for another project I have not started on yet. Before I plan much more for that, I wanted to make sure my idea would work. This project will need to add and subtract 8 bit numbers and a lookup table is one way to do that. The 8k EEPROMs I'm using have 13 address lines which allow four pairs of bits to be added with a carry bit. When I first started I fed the carry output of each pair into the carry input of the next pair. This wasted outputs and inputs. It probably would have taken a long time for the carries to propagate also. Now, it only needs nine inputs and the remaining four could be used to select functions other than adding. The data in the EEPROM was simple to generate with a small script that calculates all possible input combinations.

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