Contact layer traces to program programmable ROM

1. A device comprising:

a programmable read-only memory (ROM) circuit, comprising:

physically contiguous pairs of bit-cells, each pair of bit-cells including an active layer trace extending continuously across both of the bit-cells of the pair of bit-cells, wherein the pairs of bit-cells include:

a first pair of bit-cells comprising a contact layer point shared among the bit-cells in the first pair such that each bit-cell in the pair is programmed to a value of one; and

a second pair of bit-cells that comprises no contact layer point shared among the bit-cells in the second pair such that each bit-cell in the pair is programmed to a value of zero;

an address circuit coupled to the programmable ROM circuit and configured to address only a first bit-cell of each pair of bit-cells; and

a processor coupled to the address circuit and the programmable ROM circuit, the processor configured to use the address circuit to read data from the pairs of bit-cells of the programmable ROM circuit.

2. The device of claim 1 , wherein:

the multiple physically contiguous pairs of bit-cells comprise a plurality of non-overlapping byte-subsets of the pairs of bit-cells, each byte-subset comprising n pairs of bit-cells;

the address circuit is configured to address simultaneously the first bit-cell of each pair of bit-cells in a selected byte-subset; and

the processor is configured to read data simultaneously from the first bit-cell of each pair of bit-cells in the selected byte-subset.

3. The device of claim 2 , wherein the pairs of bit-cells of at least one byte-subset are arranged in a column.

4. The device of claim 3 , wherein two or more of the plurality of byte-subsets are arranged in a row.

5. The device of claim 4 , wherein the active layer trace across both of the bit-cells of a first pair of bit-cells of a first byte-subset in the row extends continuously across both of the bit-cells of a second pair of bit-cells of a second byte-subset in the row.

6. The device of claim 2 , wherein the number n of pairs of bit-cells of at least one byte-subset is four.

7. The device of claim 6 , wherein the programmable ROM circuit comprises one of sixteen byte-subsets and thirty-two byte-subsets.

8. The device of claim 2 , wherein:

the programmable ROM circuit comprises a first group of byte-subsets and a second group of byte-subsets;

bit-cell addresses of the first bit-cell of each pair of bit-cells of the first group of byte-subsets are contiguous;

bit-cell addresses of the first bit-cell of each pair of bit-cells of the second group of byte-subsets are contiguous; and

a first bit-cell address range of the first bit-cell of each pair of bit-cells of the first group of byte-subsets is discontiguous from a second bit-cell address range of the first bit-cell of each pair of bit-cells of the second group of byte-subsets.

9. A device comprising:

a programmable read-only memory (ROM) circuit, comprising:

a first plurality of bit-cells comprising multiple non-overlapping single-cell byte-subsets of the bit-cells, each single-cell byte-subset comprising m bit-cells;

a second plurality of bit-cells comprising multiple physically contiguous pairs of bit-cells, each pair of bit-cells including an active layer trace extending continuously across both of the bit-cells of the pair of bit-cells;

a first pair of bit-cells comprising a contact layer point shared among the bit-cells in the first pair such that each bit-cell in the pair is programmed to a value of one; and

a second pair of bit-cells that comprises no contact layer point shared among the bit-cells in the second pair such that each bit-cell in the pair is programmed to a value of zero;

the multiple physically contiguous pairs of bit-cells comprising a plurality of non-overlapping paired-cell byte-subsets of the pairs of bit-cells, each paired-cell byte-subset comprising n pairs of bit-cells;

an address circuit coupled to the programmable ROM circuit and configured to address simultaneously the bit-cells of a selected single-cell byte-subset or only a first bit-cell of each pair of bit-cells of a selected paired-cell byte-subset; and

a processor coupled to the address circuit and the programmable ROM circuit, the processor configured to use the address circuit to read data from the selected single-cell byte-subset or selected paired-cell byte-subset of the programmable ROM circuit.

10. The device of claim 9 , wherein the bit-cells of at least one single-cell byte-subset are arranged in a first column and the pairs of bit-cells of at least one paired-cell byte-subset are arranged in a second column.

11. The device of claim 10 , wherein two or more of the single-cell byte-subsets are arranged in a first row and two or more of the paired-cell byte-subsets are arranged in a second row.

12. The device of claim 11 , wherein the active layer trace across both of the bit-cells of a first pair of bit-cells of a first paired-cell byte-subset in the second row extends continuously across both of the bit-cells of a second pair of bit-cells of a second paired-cell byte-subset in the second row.

13. The device of claim 9 , wherein the number m of bit-cells of at least one single-cell byte-subset is four or the number n of pairs of bit-cells of at least one paired-cell byte-subset is four.

14. The device of claim 9 , wherein:

the programmable ROM circuit comprises a first group of paired-cell byte-subsets and a second group of paired-cell byte-subsets;

bit-cell addresses of the first bit-cell of each pair of bit-cells of the first group of paired-cell byte-subsets are contiguous and bit-cell addresses of the first bit-cell of each pair of bit-cells of the second group of paired-cell byte-subsets are contiguous; and

a first bit-cell address range of the first bit-cell of each pair of bit-cells of the first group of paired-cell byte-subsets is discontiguous from a second bit-cell address range of the first bit-cell of each pair of bit-cells of the second group of paired-cell byte-subsets.

15. A method, comprising:

initiating fabrication of a first system on a chip (SoC) based on a first Graphic Design System Information Interchange (GDSII) chip layout file, the first GDSII chip layout file defining the first SoC as comprising a programmable read-only memory (ROM) circuit that includes:

multiple physically contiguous pairs of bit-cells, each pair of bit-cells including an active layer trace extending continuously across both of the bit-cells of the pair of bit-cells; and

each pair of bit-cells comprising a contact layer point shared among the bit-cells in the pair when each bit-cell in the pair is programmed to a value of one and no contact layer point shared among the bit-cells in the pair when each bit-cell in the pair is programmed to a value of zero;

testing the first SoC;

in response to determining that firmware of the first SoC should be changed;

halting fabrication of the first SoC;

generating a new ROM image;

initiating generation of a second GDSII chip layout file defining a second SoC that differs from the first GDSII chip layout file at least in locations of the shared contact layer points of the pairs of bit-cells of the programmable ROM circuit in the first SoC and in the second SoC; and

initiating fabrication of the second SoC based on the second GDSII chip layout file.

16. The method of claim 15 , wherein the second SoC is fabricated from a partially fabricated first SoC that has not had a contact layer deposited in the programmable ROM circuit.

17. The method of claim 15 , wherein the first and second GDSII chip layout files define:

a plurality of non-overlapping byte-subsets of the pairs of bit-cells, each byte-subset comprising n pairs of bit-cells;

an address circuit configured to address simultaneously a first bit-cell of each pair of bit-cells in a selected byte-subset; and

a processor configured to read data simultaneously from the first bit-cell of each pair of bit-cells in the selected byte-subset.

18. The method of claim 17 , wherein the first and second GDSII chip layout files define:

the pairs of bit-cells of at least one byte-subset as arranged in a column;

two or more of the plurality of byte-subsets as arranged in a row; and

the active layer trace across both of the bit-cells of a first pair of bit-cells of a first byte-subset in the row as extending continuously across both of the bit-cells of a second pair of bit-cells of a second byte-subset in the row.

19. The method of claim 17 , wherein the first and second GDSII chip layout files define the number n of pairs of bit-cells of each byte-subset as four.

20. The method of claim 17 , wherein the first and second GDSII chip layout files define:

the programmable ROM circuit as comprising a first group of paired-cell byte-subsets and a second group of paired-cell byte-subsets;

the first bit-cell of each pair of bit-cells of the first group of paired-cell byte-subsets as having contiguous bit-cell addresses;

the first bit-cell of each pair of bit-cells of the second group of paired-cell byte-subsets as having contiguous bit-cell addresses; and

a first bit-cell address range of the first bit-cell of each pair of bit-cells of the first group of paired-cell byte-subsets discontiguous from a second bit-cell address range of the first bit-cell of each pair of bit-cells of the second group of paired-cell byte-subsets.