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Programmable Logic Devices 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 Dense array of AND gates Product OR gates terms Outputs Programmable Array Block Diagram for Sum of Products Form Basic Programmable Logic Organizations • Depending on which of the AND/OR logic arrays is programmable, we have three basic organizations ORGANIZATION AND ARRAY OR ARRAY PAL PROG. FIXED PROM FIXED PROG. PLA PROG. PROG. PLA Logic Implementation Key to Success: Shared Product Terms Equations F0 = A + B C Example: F1 = A C + A B F2 = B C + A B F3 = B C + A Personality Matrix Input Side: Product Inputs Outputs term 1 = asserted in term A B C F0 F 1 F 2 F 3 0 = negated in term AB 1 1 - 0 1 1 0 - = does not participate BC - 0 1 0 0 0 1 Reuse 0 1 0 0 of Output Side: AC 1 - 0 terms BC - 0 0 1 0 1 0 1 = term connected to output A 1 - - 1 0 0 1 0 = no connection to output PLA Logic Implementation Example Continued - Unprogrammed device A B C All possible connections are available before programming F0 F1 F2 F3 PLA Logic Implementation Example Continued - A B C Programmed part Unwanted connections are "blown" AB BC AC BC A Note: some array structures work by making connections rather than breaking them F0 F1 F2 F3 PLA Logic Implementation Alternative representation Unprogrammed device Short-hand notation so we don't have to draw all the wires! X at junction indicates A B C D a connection AB AB CD Notation for implementing CD F0 = A B + A B Programmed device F1 = C D + C D AB+AB CD+CD PLA Logic Implementation A B C Design Example ABC Multiple functions of A, B, C A B F1 = A B C C A F2 = A + B + C B F3 = A B C C ABC F4 = A + B + C ABC F5 = A B C ABC ABC F6 = A B C ABC ABC ABC F1 F2 F3 F4 F5 F6 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 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 PAL Logic Implementation Design Example: BCD to Gray Code Converter K-maps Truth Table AB A AB A A B C D W X Y Z CD 00 01 11 10 CD 00 01 11 10 0 0 0 0 0 0 0 0 00 0 0 X 1 00 0 1 X 0 0 0 0 1 0 0 0 1 0 0 1 0 0 0 1 1 01 0 1 X 1 01 0 1 X 0 0 0 1 1 0 0 1 0 D D 0 1 0 0 0 1 1 0 11 0 1 X X 11 0 0 X X 0 1 0 1 1 1 1 0 C C 0 1 1 0 1 0 1 0 10 0 1 X X 10 0 0 X X 0 1 1 1 1 0 1 1 1 0 0 0 1 0 0 1 B B 1 0 0 1 1 0 0 0 K-map for W K-map for X 1 0 1 0 X X X X 1 0 1 1 X X X X A A 1 1 0 0 X X X X AB AB 1 1 0 1 X X X X CD 00 01 11 10 CD 00 01 11 10 1 1 1 0 X X X X 00 0 1 X 0 00 0 0 X 1 1 1 1 1 X X X X 01 0 1 X 0 01 1 0 X 0 Minimized Functions: D D 11 1 1 X X 11 0 1 X X C C W=A+BD+BC 10 1 1 X X 10 1 0 X X X=BC Y=B+C B B Z=ABCD+BCD+AD+BCD K-map for Y K-map for Z PAL Logic Implementation Programmed PAL: A B C D A BD BC Minimized Functions: 0 W=A+BD+BC BC X=BC 0 Y=B+C 0 Z=ABCD+BCD+AD+BCD 0 B C 0 0 AB C D BCD AD BCD 4 product terms per each OR gate W X Y Z PAL Logic Implementation Code Converter Discrete Gate Implementation A A A 1 B 4 C B D 2 3 W D B C 3 B 2 C D D 4 Z D 1 5 A B 2 1 X B C 1 C 3 D C 1: 7404 hex inverters B 2 Y 2,5: 7400 quad 2-input NAND B 1 3: 7410 tri 3-input NAND 4: 7420 dual 4-input NAND 4 SSI Packages vs. 1 PLA/PAL Package! PLA Logic Implementation Another Example: Magnitude Comparator A B C D A A ABCD AB AB CD 00 01 11 10 CD 00 01 11 10 ABCD 00 1 0 0 0 00 0 1 1 1 ABCD 01 0 1 0 0 01 1 0 1 1 D D ABCD 11 0 0 1 0 11 1 1 0 1 C C AC 10 0 0 0 1 10 1 1 1 0 AC B B BD K-map for EQ K-map for NE BD A A AB AB 00 01 11 10 00 01 11 10 ABD CD CD 00 0 0 0 0 00 0 1 1 1 BCD 01 1 0 0 0 01 0 0 1 1 ABC D D BCD 11 1 1 0 1 11 0 0 0 0 C C 10 1 1 0 0 10 0 0 1 0 B B EQ NE LT GT K-map for LT K-map for GT Another Variation: Synchronous vs. Asynchronous Outputs CLK • DQ Q0 Seq N Q1 DQ Seq D Open DQ Com Reset 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. GAL22V10, GAL16V8, etc. GAL 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. GAL22V10 OLMC Structure PAL22V10 OLMC Configuration Modes • Registered Mode: active (low, high): Q’ is feedback as input only, no dedicated input in this mode • Combinational Mode: active (low, high) can feedback comb. Output (high, low) and/or dedicated input GAL16V8 OLMC Structure OE CLK 11 T 10 S 01 M 00 U vcc X AC0 AC1(n) P O T M O O U M 1 X U I/O(n) Q 1 X FROM AND ARRAY D Q XOR(n) F 10- M 11- FEEDBACK U 0-1 X 0-0 FROM ACO AC1(m) ADJ. STAGE OUTPUT(m) CLK AC1(n) OE PAL16V8 OLMC Configuration Modes Simple mode (combinational output) combinational output combinational output with feedback dedicated input Complex mode combinational output, with feedback combinational input from another OLMC Registered mode: active (low, high): Q’ is feedback as input (no dedicated input) Field Programmable Gate Arrays (FPGAs) • FPGAs have much more logic than CPLDs – 2K to >10M 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-volatile memory – Reprogramming is more difficult – Holds configuration when power is off FPGA Structure • Typical organization in 2-D array – Configurable logic blocks (CLBs) contain functional logic (could be similar to PAL22V10) • 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 Field-Programmable Gate Arrays structure • Logic blocks – To implement combinational and sequential logic • Interconnect – Wires to connect inputs and outputs to logic blocks • I/O blocks – Special logic blocks at periphery of device for external connections • Key questions: – How to make logic blocks programmable? – How to connect the wires? – After the chip has been fabbed – HW problems: 7-19, 7-20, 7-22, 7-23, 7-26 due 22/9/07