30/10/2019 https://athena.ecs.csus.edu/~changw/205/prg/3/ https://athena.ecs.csus.edu/~changw/205/prg/3/ 1/3 CSc 205 Verilog Programming #3: Adder-Subtractor (Arrays of Gates & Modules) 1. In this...

Write a Verilog program to simulate a 5-bit adder-subtractor.


30/10/2019 https://athena.ecs.csus.edu/~changw/205/prg/3/ https://athena.ecs.csus.edu/~changw/205/prg/3/ 1/3 CSc 205 Verilog Programming #3: Adder-Subtractor (Arrays of Gates & Modules) 1. In this programming assignment, we will practice the use of modules as an array! 2. Write a Verilog program to simulate a 5-bit adder-subtractor. Submit only 1 program file "add-sub.v" to your "3rdPrgAssig" folder. (Make a "V2" folder for revision 2, in the same folder to re-submit. Use "V3" for another revision, and so on.) Misplaced files may get points deducted. 3. A single Full Adder (FA) is illustrated below. Make the final simulated based on a 5-bit adder- subtractor which will have five FA's chained. The five xor gates are used to flip y bits when performing a subtraction. The 6th xor gate is used to detect an overflow condition (explained below). 4. The first carry-in bit C0 can serve as the flag to perform a subtraction if set 1. If 0, it performs addition. The truth table shows the s (sum) and cout (carry-out) bits are results of a majority function and parity check: cin x y -> cout s 0 0 0 0 0 0 0 1 0 1 0 1 0 0 1 0 1 1 1 0 1 0 0 0 1 1 0 1 1 0 1 1 0 1 0 1 1 1 1 1 Follow the diagram below to program a Full Adder. Multi-bit Adder / Subtractor (program an array of full adders) 5. Keyboard Input Examples: how to program for keyboard input. 6. The keyboard input asks for two numbers X and Y. Each ranges from 0 to 15 (by entering '00'to '15'). Afterward, a plus or minus sign ('+' or '-') should be entered to perform either an addition or subtraction. 7. To copy the demo executable and run it: atoz[193]% cp -p ~changw/html/205/prg/3/demo-a.out . atoz[194]% demo-a.out Enter X (range 00 ~ 15): 10 Enter Y (range 00 ~ 15): 03 Enter '+' or '-': + X=01010 (10) Y=00011 ( 3) C0=0 Result=01101 (+13) E = 0 atoz[195]% demo-a.out Enter X (range 00 ~ 15): 12 Enter Y (range 00 ~ 15): 13 Enter '+' or '-': https://athena.ecs.csus.edu/~changw/205/prg/3/KeyinExample 30/10/2019 https://athena.ecs.csus.edu/~changw/205/prg/3/ https://athena.ecs.csus.edu/~changw/205/prg/3/ 2/3 - X=01100 (12) Y=01101 (13) C0=1 Result=11111 (- 1) E = 0 atoz[196]% demo-a.out Enter X (range 00 ~ 15): 01 Enter Y (range 00 ~ 15): 15 Enter '+' or '-': - X=00001 ( 1) Y=01111 (15) C0=1 Result=10010 (-14) E = 0 atoz[197]% demo-a.out Enter X (range 00 ~ 15): 11 Enter Y (range 00 ~ 15): 15 Enter '+' or '-': + X=01011 (11) Y=01111 (15) C0=0 Result=11010 (- 6) E = 1 8. The ASCII value obtained from the input must be converted, e.g., if '13' is entered, it gets 49 and 51 (ASCII value), then a subtraction of 48 is needed for each to get the value of 10's and 1's. 9. The xor of the last two carries generates the E indicater. If E is 0, the sum bits are OK as a 2's complement result. If E is 1, then the final carry-out bit is needed to place in front of the result. Otherwise, the result will not be correct in the signed 2's complement bitmap. E is the true overflow indicator. overflowed.) 10. The skeleton of your program should look like this: // add-sub.v, 205 Verilog Programming Assignment #3 // can do both add & subtract on 5-bit operands // use arrays of gates and modules // // PUT YOUR NAME HERE module TestMod; parameter PLUS_SIGN = 43; parameter MINUS_SIGN = 45; parameter STDIN = 32'h8000_0000; // keyboard input channel reg [7:0] str [1:3]; // typing in, 3 chars reg [4:0] X, Y; // 5-bit X, Y to sum reg C0; // set 0/1 to do add/subtract wire [4:0] S; // 5-bit Sum to see as result wire E; // Error indicator, overflow instantiate AddSubMod (with input C0, X, and Y, output E and S) initial begin 1. prompt for keyboard entry --> $display("Enter X (range 00~15): "); get 1st character --> str[1] = $fgetc(STDIN); get 2nd character get 3rd character (Enter key) convert from 1st (10's) and 2nd (1's) chars to X 2. (repeat above for Y) 3. get a char (and the Enter key) if it is '+,' set C0 to 0 // add X and Y otherwise (assume '-'), set C0 to 1 // subtract Y from X 4. #2; // wait a bit for the add/sub to get done 5. display X, Y, S, and E (see demo runs) end endmodule 30/10/2019 https://athena.ecs.csus.edu/~changw/205/prg/3/ https://athena.ecs.csus.edu/~changw/205/prg/3/ 3/3 module AddSubMod(C0, X, Y, S, E); input C0; // single bit input input [4:0] X, Y, ... // 4-bit input items output ... output ... (multiple output lines due to size differences) ... ... use ARRAY of gates: xor my5xor [4:0] (...); and ARRAY of module instances: FullAdderMod my5FA [?:?] (...); endmodule module FullAdderMod(...); // single-bit adder module ... ... (follow the diagram) ... endmodule A List of Useful Linux and vi Commands Access Dropbox from a Linux Shell https://athena.ecs.csus.edu/~changw/class_docs/UnixVi.html https://athena.ecs.csus.edu/~changw/class_docs/AccessDropbox.html