1. Programmable logic devices
PLA circuits
Built around homogeneous arrays of elementary components that can be configured to perform logical AND and OR operations
We look at basic structures that can realize AND, OR functions (in reality PLAs are based on NAND/NOR functions in CMOS technology)
PLAs can belong to
Gate arrays, if interconnect layer is not finished
PLDs, if fuses are provided along with a full interconnect layer
FPGA are PLD

2. Programmable logic devices

3. Programmable logic devices

4. Programmable logic devices

5. Diode logic

6. Diode logic

7. Diode logic
( in the compact form, X indicates presence of a diode )

8. Diode logic Multiple functions realized by an AND-OR array
ab is “shared” by both outputs

9. Diode logic Example: PLA table: AND array: OR array:
0  complement connected;
1  true form connected;
X  no connection
OR array:
1  connection;
0  no connection

10. Diode logic
Resulting PLA:
The AND and the OR arrays are programmable

11. Diode logic
a figure
How many literals in each prime implicant?

12. PLA realization of the majority voter

13. Field-programmable arrays
Uncommitted AND/OR arrays with metal fuses that can be blown.
Unprogrammed AND array:

14. Programmed AND function A’BC’ and its compact notation
X means fuse intact (not blown)

15. Programmed AND function AB’ and its compact notation

16. Fuse-programmable OR arrays
Unprogrammed:
Programmed OR function P1+P3 and its compact notation

17. Other options in programmable devices
Output polarity options
Programmed active high
Programmed active low

18. Apply transforms to indirectly obtain the POS formula

19. Other options in programmable devices
Bidirectional pins and feedback lines
Driver enabled
Driver disabled

20. Other options in programmable devices
Bidirectional pins and feedback lines
When driver enabled, sum term Sm available as output and fed back to the AND array
This allows multilevel circuits (more than 2 levels)
When driver disabled, the IOm pin acts as external input
Example: implement a 2-bit ripple-carry adder
Use PLA with 4 inputs, 3 outputs and 2 bi-directional pins
Use one bi-directional pin for input, the other for output/feedback

21. Two-bit ripple carry adder implementation
Question: why are all the fuses left intact on product term 16?

22. Commercial PLDs
Basic PLD organization

23. Commercial PLDs
Some commercially available PLDs