1. Programmable Logic

2. Prgrammable Logic Organization
Pre-fabricated building block of many AND/OR gates (or NOR, NAND)
"Personalized" by making or breaking connections among the gates
Inputs
Dense array of
AND gates
Dense array of
OR gates
Product
terms
Outputs
Programmable Array Block Diagram for Sum of Products Form

3. Basic Programmable Logic Organizations
Depending on which of the AND/OR logic arrays is programmable, we have three basic organizations
AND ARRAY
PROG.
FIXED
OR ARRAY
ORGANIZATION
PAL
PROM
PLA

4. PLA Logic Implementation
Key to Success: Shared Product Terms
Equations
F0 = A + B C
F1 = A C + A B
F2 = B C + A B
F3 = B C + A
Example:
Personality Matrix
Input Side: F 1
Outputs
Inputs
Product t
erm A - B C 2 3
A B
B C
A C
1 = asserted in term
0 = negated in term
- = does not participate
Reuse of t
erms
Output Side:
1 = term connected to output
0 = no connection to output

5. PLA Logic Implementation
Example Continued - Unprogrammed device A B C F0 F1 F2 F3
All possible connections are available
before programming

6. PLA Logic Implementation
Example Continued -
Programmed part A B C F0 F1 F2 F3 AB BC AC
Unwanted connections are "blown"
Note: some array structures
work by making connections
rather than breaking them

7. PLA Logic Implementation
Unprogrammed device
Alternative representation for
high fan-in structures
Short-hand notation
so we don't have to
draw all the wires!
X at junction indicates
a connection
A B C D
AB+AB
CD+CD AB CD
Notation for implementing
F0 = A B + A B
F1 = C D + C D
Programmed device

8. PLA Logic Implementation
ABC A B C F1 F2 F3 F4 F5 F6
Design Example
Multiple functions of A, B, C
F1 = A B C
F2 = A + B + C
F3 = A B C
F4 = A + B + C
F5 = A  B  C
F6 = A  B  C

9. PALs and PLAs
What is difference between Programmable Array Logic (PAL) and
Programmable Logic Array (PLA)?
PAL concept — implemented by Monolithic Memories
AND array is programmable, OR array is fixed at fabrication
A given column of the OR array
has access to only a subset of
the possible product terms
PLA concept — Both AND and OR arrays are programmable

10. PALs and PLAs Of the two organizations the PLA is the most flexible
One PLA can implement a huge range of logic functions
BUT many pins; large package, higher cost
PALs are more restricted / you trade number of OR terms vs number of outputs
Many device variations needed
Each device is cheaper than a PLA

11. PAL Logic Implementation
Design Example: BCD to Gray Code Converter
K-maps
Truth Table AB CD 00 01 11 10 D B C A X 1
K-map for W Y Z A 1 B C D W X Y Z
Minimized Functions:
W = A + B D + B C
X = B C
Y = B + C
Z = A B C D + B C D + A D + B C D

12. PAL Logic Implementation
Programmed PAL:
A B C D
A B C D A BD BC B C
BCD AD
W X Y Z
Minimized Functions:
W = A + B D + B C
X = B C
Y = B + C
Z = A B C D + B C D + A D + B C D
4 product terms per each OR gate

13. PAL Logic Implementation
Code Converter Discrete Gate Implementation B C A D W X Y 2 Z 1 4 3 5
1: 7404 hex inverters
2,5: 7400 quad 2-input NAND
3: 7410 t
ri 3-input NAND
4: 7420 dual 4-input NAND
4 SSI Packages vs. 1 PLA/PAL Package!

14. PLA Logic Implementation
Another Example: Magnitude Comparator EQ NE LT GT
ABCD AC BD
ABD
BCD
ABC
A B C D A
K-map for EQ 1 AB CD 00 01 11 10 D B C GT L T NE

15. Complex Programmable Logic Devices
Complex PLDs typically combine PAL combinational logic with FFs
Organized into logic blocks
Fixed OR array size
Combinational or registered output
Some pins are inputs only
Usually enough logic for simple counters, state machines, decoders, etc.
e.g. 22G10, 20V8, etc.

16. 16V8 CPLD
OLMC (Output Logic MacroCell) has OR, FF, output multiplexer and I/O control logic.
Note that OLMC output is fed back to input matrix for use in other OLMCs.

17. OLMC Structure 11 10 01 00 T S M U X O 1 P F 10- 11- 0-1 0-0 D Q vcc
XOR(n)
FROM
AND
ARRAY
FEEDBACK
CLK OE
I/O(n)
ADJ. STAGE
OUTPUT(m)
AC0
AC1(n)
ACO
AC1(m)

18. Field Programmalble Gate Arrays (FPGAs)
FPGAs have much more logic than CPLDs
2K to >50M equivalent gates
Requires different architecture
FPGAs can be RAM-based or Flash-based
RAM FPGAs must be programmed at power-on
External memory needed for programming data
May be dynamically reconfigured
Flash FPGAs store program data in non-volitile memory
Reprogramming is more difficult
Holds configuration when power is off

19. FPGA Structure Typical organization in 2-D array
Configurable logic blocks (CLBs) contain functional logic
Combinational functions plus FFs
Complexity varies by device
CLB interconnect is either local or long line
CLBs have connections to local neighbors
Horizontal and vertical channels use for long distance
Channel intersections have switch matrix
IOBs (I/O logic Blocks) connect to pins
Usually have some additional C.L./FF in block

20. FPGA Structure CLB CLB CLB CLB CLB CLB CLB CLB CLB CLB CLB CLB CLB CLB
Input/Output
Block
IOB
IOB
IOB
IOB
CLB
CLB
CLB
CLB
Switch
Matrix SM SM SM
CLB
CLB
CLB
CLB SM SM SM
IOB
IOB
CLB
CLB
CLB
CLB
Configurable
Logic
Block SM SM SM
CLB
CLB
CLB
CLB
IOB

21. FPGA IOB Structure

22. FPGA CLB Structure