Lecture 7 1

Introduction  Comparison of Standard Logic Circuits and Programmable Logic Circuits  Evolution and Overview of PLC:  PROM, PLA, PAL  CPLD  FPGA 1/13 Resource: Xilinx, Aleksandra Kovacevic

Logic Circuits Standard Logic CircuitsProgrammable Logic Circuits Realize single function or set of functions, once defined and with no possibility of changing. Contains great number of standard logic circuits Possibility of realizing many various functions Hardware can configure any time by user programming. 2/13

Standard Logic Circuits Appropriate for many applications because of possibility of realization in mass production for relative low cost. Standard logic circuits are sometimes the best choice in high-performance devices. Disadvantage: Not permitting design updates (function changes) with no hardware replacement necessary. 3/13

Field- Programmable Logic Devices Component function is defined by users program. Advantages:  Ease of design changes  Reduce prototype-product time  Large scale integration (over gates)  Reliability increased, low financial risk  Smaller device, low start-up cost 4/13

FPLDs Representatives PLA - Programmable Logic Arrays PAL - Programmable Array Logic CPLD - Complex Programmable Logic Devices FPGA - Field Programmable Gate Arrays PLD Programmable logic device 5/13

Evolution of PLD: Why not PROM? A special device (called a burner), used to put the information, supplies an electrical current to specific cells in the ROM that effectively blows a fuse in them = burning the PROM. From that point on, chip is read-only. PROM was the first type of user-programmable chip; address lines = logic circuit inputs data lines = logic circuit outputs PROMs are inefficient architecture for realizing logic circuit: Logic functions rarely require more than few product terms PROM contains a full decoder for its address inputs. 6/13

Evolution of PLD: PLA PLA was the first device developed for implementing Consist of two levels of logic gates - programmable “wired” AND-plane & OR-plane Note: Drawbacks: Expensive to manufacture Offered somewhat poor speed-performance 7/13

Evolution of PLD: PAL ™ Overcame weaknesses of PLA Single level of programmability - consists of a programmable “wired” AND-plane & fixed OR- gates Simpler to program and cheaper implementation Limited numbers of terms in each output Note: PAL is a trademark of Advanced Micro Devices 8/13

Evolution of PLD: Register PLA Contain flip flops connected to the OR gate outputs Importance: Profound effect on digital hardware design Basis for more sophisticated architectures sequential circuits can be realized 9/13

Evolution of PLD: CPLD Technology advanced possibility to produce devices with higher capacity than SPLDs. Structure grows too quickly in size as the number of inputs is increased Integrating multiple SPLDs onto a single chip - the only feasible way to provide large capacity devices based on SPLD Programmably connect the SPLD blocks together Logic capacity up to the equivalent of about 50 typical SPLD devices Logic Array Blocks - Complex SPLD- like structure Programmable Interconnect Array - Capable of connecting any LAB input or output to any other LAB 10/13

... and finally... 11/13

Evolution of PLD: FPGA Difficult extending CPLDs architectures to higher densities - a different approach is needed FPGAs comprise an array of uncommited circuit elements, called logic blocks, and interconnect resources FPGA configuration is performed through programming by the end user. Xilinx FPGA Configuration contains a set of basic functions (gates, FFs, memory cells) 12/13

14 * A field-programmable gate array (FPGA) is a logic device that contains a two-dimensional array of generic logic cells and programmable switches. Resource1: FPGA Prototyping By Verilog Examples, Pong P. Chu, Wiley, 2008, Resource2: Xilinx DS099 Design Specification,

15 * A logic cell can be configured (i.e., programmed) to perform a simple function * A programmable switch can be customized to provide interconnections among the logic cells * A custom design can be implemented by specifying the function of each logic cell and selectively setting the connection of each programmable switch * Once the design and synthesis are completed, we can use a simple adaptor cable to download the desired logic cell and switch configuration to the FPGA device * Since this process can be done "in the field" rather than "in a fabrication facility (fab)," the device is known as field programmable.

16 * A logic cell usually contains a small configurable combinational circuit with a D-type flip-flop (DFF) * The most common method to implement a configurable combinational circuit is a look-up table (LUT). An n-input LUT can be considered as a small 2 n -by-1 memory * By properly writing the memory content, we can use a LUT to implement any n-input combinational function

17 * Most FPGA devices also embed certain macro cells or macro blocks, * These are designed and fabricated at the transistor level and their functionalities complement the general logic cells * Commonly used macro cells include memory blocks, combinational multipliers, clock management circuits, and I/0 interface circuits * Advanced FPGA devices may even contain one or more prefabricated processor cores

18 * Logic cell * The most basic element of the Spartan-3 device is a logic cell (LC), which contains a four-input LUT and a DFF * Slice * In Xilinx terms, two logic cells are grouped to form a slice * CLB * Four slices are grouped to form a configurable logic block (CLB) * Macro Cell * The Spartan-3 device contains four types of macro blocks: combinational multiplier, block RAM, digital clock manager (DCM), and input/output block (IOB)

19 * Array Multiplier * The combinational multiplier accepts two 18-bit numbers as inputs and calculates the product * Block RAM * The block RAM is an 18K-bit synchronous SRAM that can be arranged in various types of configurations * DCM * A DCM uses a digital-delayed loop to reduce clock skew and to control the frequency and phase shift of a clock signal * IOB * An IOB controls the flow of data between the device's I/0 pins and the internal logic. It can be configured to support a wide variety of I/0 signaling standards.

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24 * Spartan-3 FPGA QFP Package for Part Number XC3S400-4PQ208C

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26 1. Xilinx Spartan-3 XC3S200 FPGA device (XC3S200FT256) 2. 2M-bit Xilinx XCF02S platform flash configuration PROM 3. Jumper to select the configuration source 4. Two 256K-by-16 asynchronous SRAM devices (ISSI IS61LV25616AL-10T) VGA display port 6. RS-232 serial port 7. RS-232 transceiverl voltage-level convertor 8. Second RS-232 transmit and receive channel 9. PSI2 mouse/keyboard port 10. Four-digit seven-segment LED display 11. Eight slide switches 12. Eight discrete LED outputs 13. Four momentary-contact pushbutton switches MHz crystal oscillator clock source 15. Socket for an auxiliary crystal oscillator clock source 16. Jumper to select an FPGA configuration mode 17. Pushbutton switch to force FPGA reconfiguration 18. LED to indicate whether the FPGA is successfully configured pin expansion connector 1 (labeled B1) pin expansion connector 2 (labeled A2) pin expansion connector 3 (labeled A1 ) 22. JTAG connector for Digilent download cable 23. Digilent low-cost download cable (included in the S3 kit but not shown in Figure 2.3) 24. JTAG port (to be used with the Xilinx Parallel Cable IV and MultiPRO Desktop Tool,which are not included in the S3 kit) 25. Power connector for an unregulated 5-V power supply (included in the S3 kit) 26. Power-on LED indicator V voltage regulator V voltage regulator V voltage regulator 30. Selector for PS2 port voltage supply (3.3 or 5 V)