Lab1 - Xilinx
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1. inN is optional and is selection buf not instance name out1 out2 out2 input bufifO bufifl notifO notif1 instance name outputA inputB controlC pullup pulldown instance name output A One can also have multiple instances of the same type of gate in one construct separated by a comma such as and inst1 out11 in11 in12 inst2 out21 in21 in22 in23 inst3 out31 in31 in32 in33 The language also allows the delays to be expressed when instantiating gates The delay expressed is from input to output The delays can be expressed in form of rise fall and turn off delays one two or all three types of delays can be expressed in a given instance expression The turn off delay is applicable to gates whose output can be turned OFF e g notif1 For example and 5 Al Out inl in2 the rise and fall delays are 5 units and 2 5 A2 out2 inl in2 the rise delay is 2 unit and the fall delay is 5 units notifl 2 5 4 A3 out3 in2 ctrl the rise delay is 2 the fall delay is 5 and the turn off delay is 4 unit The gate level modeling is useful when a circuit is a simple combinational as an example a multiplexer Multiplexer is a simple circuit which connects one of many inputs to an output In this part you will create a simple 2 to 1 multiplexer and extend the design to multiple bits N 3 1 2 xilinx com uni it v a apain Com XILINX copyright 2013 Xilin2. An un illuminated seven segment display and nine illumination patterns corresponding to decimal digits Four digit Seven Segment Display Individual cathodes Reference Nexys3 Reference Manual The anodes of the seven LEDs forming each digit are tied together into one common anode circuit node but the LED cathodes remain separate The common anode signals are available as four digit enable input signals to the 4 digit display The cathodes of similar segments on all four displays are connected into seven circuit nodes labeled CA through CG so for example the four D cathodes from the four digits are grouped together into a single circuit node called CD These seven cathode signals are available as inputs to the 4 digit display This signal connection scheme creates a multiplexed display where the cathode signals are common to all digits but they can only illuminate the segments of the digit whose corresponding anode signal is asserted N 3 1 8 xilinx com uni it v a pG inson XILINX copyright 2013 Xilinx Lab Workbook Modeling Concepts 3 3V P17 aa P18 ae H N16 ANO IZI 21 ZT ZI ELERESE IY T18 U17 U18 M14 N14 L14 M13 7 seg Display Reference Nexys3 Reference Manual A scanning display controller circuit can be used to show a four digit number on this display This circuit drives the anode signals and corresponding cathode patterns of each digit in a repea
3. 3 1 3 Add the UCF file created in 1 1 to the project Assign SWO and SW1 to x and y SW7 to s and LEDO to m 3 1 4 Synthesize the design 3 1 5 Implement the design 3 1 6 Generate the bitstream download it into the Nexys3 board and verify the functionality 3 2 Create a two bit wide 2 to 1 multiplexer using behavioral modeling 3 2 1 Open PlanAhead and create a blank project project called lab1_3_2 3 2 2 Create and add the Verilog module with two bit input x 1 0 y 1 0 a one bit select input s and two bit output m 71 0 using behavioral modeling 3 2 3 Add the UCF file to the project that you had created in 1 2 Assign SWO and SW1 to x 1 0 SW2 and SW3 to y 1 0 SW7 to s and LEDO and LED7 to m 1 0 3 2 4 Synthesize the design 3 2 5 Implement the design 3 2 6 Generate the bitstream download it into the Nexys3 board and verify the functionality Mixed design Style Modeling Part 4 Complex systems can be described in Verilog HDL using mixed design style modeling This modeling style supports hierarchical description The design can be described using Build in gate primitives gate level modeling covered in Part 1 Dataflow modeling covered in Part 2 Behavioral modeling covered in Part 3 N 3 1 6 Xilinx uni it a apain Com XILINX copyright 2013 Xilinx Lab Workbook Modeling Concepts Module instantiation Combinations of the above Interconnections between various objec
4. Depending on the input type a type conversion may be needed If want to display a binary coded decimal BCD using 4 bit input a BCD to 7 segment decoder is required The table below shows the bit pattern you need to put to display a digit note that to turn ON a segment you need to put logic 0 on the segment and the anode of the display needs to be driven logic 0 on this board g XI LI NX w a Nexys3 1 7 copyright 2013 Xilinx Modeling Concepts Lab Workbook Input a b c d e f g 0000 0 0 0 0 0 0 1 0001 1 0 0 1 1 1 1 0010 0 0 1 0 0 1 0 0011 0 0 0 0 1 1 0 0100 1 0 0 1 1 0 0 0101 0 1 0 0 1 0 0 0110 0 1 0 0 0 0 0 0111 0 0 0 1 1 1 1 1000 0 0 0 0 0 0 0 1001 0 0 0 0 1 0 0 1010 to X X X X X X x 1111 Where x is don t care The Nexys3 board contains a four digit common anode seven segment LED display Each of the four digits is composed of seven segments arranged in a pattern shown below with an LED embedded in each segment Segment LEDs can be individually illuminated so any one of 128 patterns can be displayed on a digit by illuminating certain LED segments and leaving the others dark Of these 128 possible patterns the ten corresponding to the decimal digits are the most useful Ny Common anode iik auz am AN a II I TEI ELGER IO J IE J d l CA CB CC CD CE CF CG DP I il l puan I J i a OO pi O C C TE anu E I CI a E m a
5. IN scalar net declaration wire 3 0 SUM A B vector nets declaration assign COUT SUM A B CIN A and B vectors are added with CIN and the result is assigned to a concatenated vector of a scalar and vector nets Note that multiple continuous assignment statements are not allowed on the same destination net 2 1 Connect input switches to output LEDs using dataflow modeling 2 1 1 Open PlanAhead and create a blank project project called lab1_2 1 2 1 2 Create and add the Verilog module with 8 inputs x_in and 8 outputs y_out using dataflow modeling Use vector assignment statement as we do not need to do any processing between SW inputs 2 1 3 Create and add the UCF file to the project Assign SW7 SWO to x_inand LED7 LEDOto y_out 2 1 4 Synthesize the design 2 1 5 Implement the design 2 1 6 Generate the bitstream download it into the Nexys3 board and verify the functionality 2 2 Model a two bit wide 2 to 1 multiplexer using dataflow modeling with net delays of 3 ns 2 2 1 Open PlanAhead and create a blank project project called lab1_2 2 2 2 2 Create and add the Verilog module with two 2 bit inputs x 7 0 y 1 0 a one bit select input s and two bit output m 1 0 using dataflow modeling Each assignment statement should have 3 units delay N 3 1 4 xilinx com uni it v a apain Com XILINX copyright 2013 Xilinx Lab Workbook Modeling Concepts As an example a one bit 2 to 1
6. Lab Workbook Modeling Concepts Modeling Concepts Introduction Verilog HDL modeling language supports three kinds of modeling styles gate level dataflow and behavioral The gate level and datafow modeling are used to model combinatorial circuits whereas the behavioral modeling is used for both combinatorial and sequential circuits This lab illustrates the use of all three types of modeling by creating simple combinatorial circuits targeting Nexys3 board and using the PlanAhead software tool Please refer to the PlanAhead tutorial on how to use the PlanAhead tool for creating projects and verifying digital circuits The Nexys3 board has the following features 16Mbyte Cellular RAM x16 16Mbytes SPI quad mode PCM non volatile memory 16Mbytes parallel PCM non volatile memory 10 100 Ethernet PHY USB UART and USB HID port for mouse keyboard 8 bit VGA port 100MHz CMOS oscillator 72 O s routed to expansion connectors GPIO includes 8 LEDs 5 buttons 8 slide switches and 4 digit seven segment display The Nexys3 board is shown below Power Select Power Pmod Done Power Connectors JTAG panes Jumper Good LED Pe sill LED Header Adept gt p USB Port af p Ja Reset DONE z Button 10 100 Ethernet Port 3 J oS pan BUH 7 seg es Doms Er 27 ee IETEN Display i ra gt j gt st DIGILENT f BEYOND Tiikonmx a USB HID gt Le prio Sgn BMS RED C OE T Spey m USB Host Port soon han mm
7. e TET Ea Dama i a E Am EN gt k MER UART IN ae LEDs Slide switches Push buttons www xilinx com university Nexys3 1 1 gt Xl LI NX xup xilinx com copyright 2013 Xilinx Modeling Concepts Lab Workbook Objectives After completing this lab you will be able to Create scalar and wide combinatorial circuits using gate level dataflow and behavioral modeling Write models to read switches and push buttons and output on LEDs and 7 segment displays Simulate and understand the design output Create hierarchical designs Synthesize implement and generate bitstreams Download bitstreams into the board and verify functionality Gate level Modeling Part 1 Verilog HDL supports built in primitive gates modeling The gates supported are multiple input multiple output tristate and pull gates The multiple input gates supported are and nand or nor xor and xnor whose number of inputs are two or more and has only one output The multiple output gates supported are buf and not whose number of output is one or more and has only one input The language also supports modeling of tri state gates which include bufif0 bufif1 notif0 and notifl These gates have one input one control signal and one output The pull gates supported are pullup and pulldown with a single output no input only The basic syntax for each type of gates with zero delays is as follows and nand or nor xor xnor instance name out in1
8. e behavioral modeling supports both combinatorial and sequential circuits design In this lab you used the behavioral modeling for the combinatorial circuits design In next few labs you will be using dataflow modeling for designing various combinatorial circuits and starting with Lab 7 you will use the behavioral modeling to design sequential circuits XILINX oi Nexys3 1 9 copyright 2013 Xilinx
9. ify the functionality Dataflow Modeling Part 2 Dataflow modeling style is mainly used to describe combinational circuits The basic mechanism used is the continuous assignment In a continuous assignment a value is assigned to a data type called net The syntax of a continuous assignment is assign delay LHS_net RHS_ expression XILINX on Nexys3 1 3 copyright 2013 Xilinx Modeling Concepts Lab Workbook Where LHS_net is a destination net of one or more bit and RHS_expression is an expression consisting of various operators The statement is evaluated at any time any of the source operand value changes and the result is assigned to the destination net after the delay unit The gate level modeling examples listed in Part 1 can be described in dataflow modeling using the continuous assignment For example assign outl inl amp in2 perform and function on in1 and in2 and assign the result to out1 assign out2 not inl assign 2 z 0 ABAR amp BBAR amp EN perform the desired function and assign the result after 2 units The target in the continuous assignment expression can be one of the following 1 A scalar net e g 1 and 2 examples above 2 Vector net 3 Constant bit select of a vector e g 3 example above 4 Constant part select of a vector 5 Concatenation of any of the above Let us take another set of examples in which a scalar and vector nets are declared and used wire COUNT C
10. multiplexer can be described as follows assign 3 m s amp x s amp y 3 units delay 2 2 3 Create and add the UCF file to the project Assign SW0O and SW1 to x 1 0 SW2 and SW3 to y 1 0 SW7 to s and LEDO and LED1 to m 1 0 2 2 4 Add the provided testbench mux_2bit_2_to_1_dataflow_tb v to the project 2 2 5 Simulate the design for 100 ns and analyze the output 2 2 6 Synthesize the design 2 2 7 Implement the design 2 2 8 Generate the bitstream download it into the Nexys3 board and verify the functionality Behavioral Modeling Part 3 Behavioral modeling is used to describe complex circuits It is primarily used to model sequential circuits but can also be used to model pure combinatorial circuits The mechanisms statements for modeling the behavior of a design are initial Statements always Statements A module may contain an arbitrary number of initial or always statements and may contain one or more procedural statements within them They are executed concurrently i e to model parallelism such that the order in which statements appear in the model does not matter with respect to each other whereas the procedural statements are executed sequentially i e the order in which they appear does matter Both initial and always statements are executed at time 0 and then only always statements are executed during the rest of the time The syntax is as follows initial timing_control procedural_statement
11. s always timing_control procedural_statements where a procedural_ statement is one of procedural assignment conditional_ statement case_statement loop_ statement wait_statement The initial statement is non synthesizable and is normally used in testbenches The always statement is synthesizable and the resulting circuit can be a combinatorial or sequential circuit In order for the model to generate a combinatorial circuit the always block i should not be edge sensitive ii every branch of the conditional statement should define all output and iii every case of case statement should define all output and must have a default case More detailed coverage of this topic is covered in Lab 7 The destination LHS should be of reg type either scalar or vector For example reg m scalar reg type reg 7 0 switches vector reg type Here is an example of a 2 to 1 multiplexer model Note that begin and end statements in this example are redundant They are included for better readability XILINX oi Nexys3 1 5 copyright 2013 Xilinx Modeling Concepts Lab Workbook reg m always x or y or s begin if s 0 m y else end 3 1 Create a 2 to 1 multiplexer using behavioral modeling 3 1 1 Open PlanAhead and create a blank project project called lab1_3_1 3 1 2 Create and add the Verilog module with three inputs x y s and one output m using behavioral modeling Use the example code given above
12. ting continuous succession at an update rate that is faster than the human eye can detect If the update or refresh rate is slowed to around 45 hertz most people will begin to see the display flicker You will design and use the scanning circuit starting with Lab 8 Architecture Wizard and CoreGEN 4 2 1 Open PlanAhead and create a blank project project called lab1_4 2 4 2 2 Create a top level Verilog module named bcdto7segment_dataflow with 4 bit data input x 3 0 anode enable output signals an 3 0 and 7 bit output seg 6 0 using dataflow modeling Hint You will have to derive seven expressions for the 7 segments on paper Assign appropriate logic to an 3 0 in the model so you can display only on the right most display 4 2 3 Create and add the UCF file to the project Assign SW3 SWO to x 3 0 Assign SEGO to seg 6 0 and pins P17 P18 N15 N16 to an3 an2 an1 an0 Refer to the board s user s manual and master ucf file provided in the sources directory 4 2 4 Synthesize the design 4 2 5 Implement the design 4 2 6 Generate the bitstream download it into the Nexys3 board and verify the functionality Conclusion In this lab you created PlanAhead projects to develop various models You implemented the design and verified the functionality in hardware as well as simulation You learned three modeling styles The gate level and dataflow modeling are primarily used for the combinatorial circuits whereas th
13. ts are done through nets of type wire Nets may be scalar or vector For example wire y scalar net wire 3 0 sum vector net In absence of size the net is assumed to be the scalar type As an example of a mixed style modeling following diagram shows how one can build a 3 to1 multiplexer using multiple instances of 2 to 1 multiplexer It also shows the symbol and the truth table s s0 In the above diagram u v w are data inputs whereas SO S1 are select signals and the output is m It uses two instances of 2 to 1 multiplexer 4 1 Model a 3 to 1 multiplexer using 2 to 1 multiplexers 4 1 1 Open PlanAhead and create a blank project project called lab1_4 1 4 1 2 Create a top level Verilog module with three data inputs u y w two select inputs s0 s1 and one bit output m using the previously defined 2 to 1 multiplexer You can use any style designed 2 to 1 multiplexer 1 1 2 1 or 3 1 Wire them up as shown in the above diagram 4 1 3 Add the used 2 to 1 model file to the project 4 1 4 Create and add the UCF file to the project Assign SW0 SW1 and SW2to u y and w respectively SW3 to s0 SW4 to s1 and LEDO to m 4 1 5 Synthesize and implement the design 4 1 6 Generate the bitstream download it into the Nexys3 board and verify the functionality 4 2 Model a BCD to 7 Segment Decoder A 7 segment display consists of seven segments numbered a to g which can be used to display a character
14. x Lab Workbook Modeling Concepts 1 1 Create a 2 to 1 multiplexer using gate level modeling OTL tore 1 1 1 Open PlanAhead and create a blank project project called lab1_1_1 refer Step 1 of the PlanAhead Tutorial 1 1 2 Create and add the Verilog module with three inputs x y s and one output m using gate level modeling refer Step 1 of the PlanAhead Tutorial 1 1 3 Create and add the UCF file to the project Assign SWO and SW1 to x and y SW7 to s and LEDO to m refer Step 2 of the PlanAhead Tutorial 1 1 4 Synthesize the design refer Step 4 of the PlanAhead Tutorial 1 1 5 Implement the design refer Step 5 of the PlanAhead Tutorial 1 1 6 Generate the bitstream download it into the Nexys3 board and verify the functionality refer Step 6 of the PlanAhead Tutorial for steps involved in creating and downloading the bitstream 1 2 Create a two bit wide 2 to 1 multiplexer using gate level modeling 1 2 1 Open PlanAhead and create a blank project project called lab1_1_ 2 1 2 2 Create and add the Verilog module with two 2 bit inputs x 1 0 y 1 0 a one bit select input s and two bit output m 1 0 using gate level modeling 1 2 3 Create and add the UCF file to the project Assign SWO and SW1 to x 1 0 SW2 and SW3 to y 1 0 SW7 to s and LEDO and LED7 to m 1 0 1 2 4 Synthesize the design 1 2 5 Implement the design 1 2 6 Generate the bitstream download it into the Nexys3 board and ver
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