Browse Prior Art Database

Read Only Store Using Large Scale Integration

IP.com Disclosure Number: IPCOM000077945D
Original Publication Date: 1972-Oct-01
Included in the Prior Art Database: 2005-Feb-25
Document File: 2 page(s) / 60K

Publishing Venue

IBM

Related People

Schmidt, SA: AUTHOR [+2]

Abstract

A read-only store (ROS) is implemented by using standard large scale integration logic blocks. This eliminates need for unique logic chips, special packaging and power supplies.

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Read Only Store Using Large Scale Integration

A read-only store (ROS) is implemented by using standard large scale integration logic blocks. This eliminates need for unique logic chips, special packaging and power supplies.

The implementation shown in Fig. 1 is advantageous when the selected logic family permits dotting the outputs of logic blocks such as blocks 10. Logic blocks (2N) as represented by block 20, each having N inputs, connect N input address lines 30 to 2 drive lines 40. Only one drive line is active at a time. The active drive line is connected to one or more logic blocks 10 which function as isolation blocks. Output lines 50 connected or not connected to blocks 10 have one and zero bits, respectively. This relationship can be reversed, depending upon whether or not a single output line has more one's than zero's. The maximum number of isolation blocks needed is thus one-half the number of bits in the array. This ratio will decrease in some cases, i.e., if the array is mostly one's or zero's.

If the logic family does not permit dotting the logic block outputs, the ROS can be implemented as in Fig. 2. Again, only one drive line 40 is active at a time. Each output line 50 is connected to the output of an OR circuit 15. The output is a one, if a drive line is connected to its associated OR circuit 15 and is selected. The output is zero, if a selected drive line is not connected to the associated OR circuit. The one and zero output relationships can b...