\n| Tri-state row control<\/td>\n | \u2705 Implemented<\/td>\n | Uses generate<\/code> block for clean row drive logic<\/td>\n<\/tr>\n\n| Keypad decoding<\/td>\n | \u2705 Implemented<\/td>\n | Covers full 4\u00d74 matrix with layout inversion<\/td>\n<\/tr>\n | \n| Debounce (1ms sampling)<\/td>\n | \u2705 Implemented<\/td>\n | stable_cnt<\/code> logic at 50MHz<\/td>\n<\/tr>\n\n| Debounce (3-cycle stable)<\/td>\n | \u2705 Implemented<\/td>\n | key_valid_buf<\/code> shift register<\/td>\n<\/tr>\n\n| Valid signal extension<\/td>\n | \u2705 Implemented<\/td>\n | io_valid_shift<\/code> prolongs io[12]<\/code><\/td>\n<\/tr>\n\n| Debug output via LEDs<\/td>\n | \u2705 Implemented<\/td>\n | LEDR[9:5] = io[12:8]<\/code> shows keycode and valid flag<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\nkeypad_scan.sv<\/h4>\nmodule keypad_scan (\n input logic clk, \/\/ System clock input\n input logic n_rst, \/\/ Active-low asynchronous reset\n inout tri [3:0] row_out, \/\/ Row outputs to keypad (tri-state controlled)\n input logic [3:0] col, \/\/ Column inputs from keypad\n output logic [12:8] io, \/\/ Output: io[11:8] = keycode, io[12] = key_valid\n output logic [9:0] LEDR \/\/ Debug LEDs\n);\n\n \/\/ === Internal Signals ===\n logic [1:0] row_idx; \/\/ Current row index for scanning (0\u20133)\n logic [3:0] row_drive; \/\/ Active-low row drive control\n logic [3:0] keycode; \/\/ Raw decoded key value from keypad\n logic key_valid; \/\/ Indicates a keypress was detected\n\n \/\/ === Debounce Buffers ===\n logic [2:0] key_valid_buf; \/\/ Shift register for key_valid debounce\n logic [3:0] keycode_buf; \/\/ Stable keycode output after debounce\n\n \/\/ === Output Valid Extension ===\n logic [4:0] io_valid_shift; \/\/ Extends io[12] signal for multiple cycles\n assign io[12] = |io_valid_shift; \/\/ Valid if any bit in shift register is high\n assign io[11:8] = keycode_buf; \/\/ Output stable keycode\n assign LEDR[9:5] = io[12:8]; \/\/ Debug: show keycode and valid flag\n\n \/\/ === Tri-State Row Output Control ===\n \/\/ Drive one row low at a time, others remain high-Z\n assign row_out[0] = (row_drive[0]) ? 1'bz : 1'b0;\n assign row_out[1] = (row_drive[1]) ? 1'bz : 1'b0;\n assign row_out[2] = (row_drive[2]) ? 1'bz : 1'b0;\n assign row_out[3] = (row_drive[3]) ? 1'bz : 1'b0;\n\n \/\/ === Row Scanning Logic ===\n \/\/ Rotates row index every 1ms to scan keypad\n always_ff @(posedge clk or negedge n_rst) begin\n if (!n_rst)\n row_idx <= 2'd3; \/\/ Start from row 3\n else if (is_stable)\n row_idx <= (row_idx == 0) ? 2'd3 : row_idx - 1; \/\/ Rotate rows\n end\n\n \/\/ === Row Drive Control ===\n \/\/ Only one row is actively driven low at a time\n always_comb begin\n row_drive = 4'b1111; \/\/ Default: all rows high-Z\n row_drive[row_idx] = 1'b0; \/\/ Drive current row low\n end\n\n \/\/ === Key Detection and Decoding ===\n \/\/ Detects keypress and maps row\/column pair to keycode\n always_ff @(posedge clk or negedge n_rst) begin\n if (!n_rst) begin\n keycode <= 4'h0;\n key_valid <= 1'b0;\n end else if (is_stable) begin\n key_valid <= 1'b0;\n for (int j = 3; j >= 0; j--) begin\n if (!col[j]) begin \/\/ Active-low column detected\n \/\/ Decode row\/column pair into keycode\n case ({row_idx, j[1:0]})\n 4'b1111: keycode <= 4'h1;\n 4'b1110: keycode <= 4'h2;\n 4'b1101: keycode <= 4'h3;\n 4'b1100: keycode <= 4'hA;\n 4'b1011: keycode <= 4'h4;\n 4'b1010: keycode <= 4'h5;\n 4'b1001: keycode <= 4'h6;\n 4'b1000: keycode <= 4'hB;\n 4'b0111: keycode <= 4'h7;\n 4'b0110: keycode <= 4'h8;\n 4'b0101: keycode <= 4'h9;\n 4'b0100: keycode <= 4'hC;\n 4'b0011: keycode <= 4'hE;\n 4'b0010: keycode <= 4'h0;\n 4'b0001: keycode <= 4'hF;\n 4'b0000: keycode <= 4'hD;\n default: keycode <= 4'h0;\n endcase\n key_valid <= 1'b1; \/\/ Mark key as valid\n end\n end\n end\n end\n\n \/\/ === Debounce Timer ===\n \/\/ Waits 1ms before sampling key state (50MHz clock \u2192 50,000 cycles)\n logic [15:0] stable_cnt;\n logic is_stable;\n\n always_ff @(posedge clk or negedge n_rst) begin\n if (!n_rst) begin\n stable_cnt <= 16'd0;\n is_stable <= 1'b0;\n end else if (stable_cnt == 16'd49999) begin\n is_stable <= 1'b1; \/\/ 1ms elapsed\n stable_cnt <= 16'd0;\n end else begin\n stable_cnt <= stable_cnt + 1;\n is_stable <= 1'b0;\n end\n end\n\n \/\/ === Debounce and Output Latching ===\n \/\/ Latches keycode only if key_valid is high for 3 consecutive samples\n always_ff @(posedge clk or negedge n_rst) begin\n if (!n_rst) begin\n key_valid_buf <= 3'b000;\n keycode_buf <= 4'h0;\n io_valid_shift <= 5'b00000;\n end else begin\n \/\/ Shift in current key_valid\n key_valid_buf <= {key_valid_buf[1:0], key_valid};\n\n \/\/ If key_valid is stable for 3 cycles, latch keycode\n if (key_valid_buf == 3'b111)\n keycode_buf <= keycode;\n\n \/\/ Extend io[12] signal for visibility (5-cycle pulse)\n io_valid_shift <= {io_valid_shift[3:0], (key_valid_buf == 3'b111)};\n end\n end\nendmodule\n<\/code><\/pre>\nkeypad_scan.qsf<\/h4>\n########## FPGA INFO\nset_global_assignment -name FAMILY "MAX 10"\nset_global_assignment -name DEVICE 10M50DAF484C7G\n\n########## top module\nset_global_assignment -name TOP_LEVEL_ENTITY keypad_scan\n\n########## CLOCK 10MHz ADC, and 2 50MHz clock source\n#set_instance_assignment -name IO_STANDARD "3.3-V LVTTL" -to clk_adc\nset_instance_assignment -name IO_STANDARD "3.3-V LVTTL" -to clk\n#set_instance_assignment -name IO_STANDARD "3.3-V LVTTL" -to clk2\n#set_location_assignment PIN_N5 -to clk_adc\nset_location_assignment PIN_P11 -to clk\nset_location_assignment PIN_N14 -to clk2\n\n########## RESET button & unused button (n_rst, KEY1)\nset_instance_assignment -name IO_STANDARD "3.3 V SCHMITT TRIGGER" -to n_rst\nset_instance_assignment -name IO_STANDARD "3.3 V SCHMITT TRIGGER" -to key1\nset_location_assignment PIN_B8 -to n_rst\nset_location_assignment PIN_A7 -to key1\n\n#===========================================================================\n################### Keypad USed Pins ###########\n### keypad scan row: row[3:0], tri-state output as OC\n# row scan signal out, row[3:0]\uff08tri-state io, set 'z' as OC cut-off\uff09\nset_location_assignment PIN_AA12 -to row_out[3]\nset_location_assignment PIN_AA11 -to row_out[2]\nset_location_assignment PIN_Y10 -to row_out[1]\nset_location_assignment PIN_AB9 -to row_out[0]\nset_instance_assignment -name IO_STANDARD "3.3-V LVTTL" -to row_out[3]\nset_instance_assignment -name IO_STANDARD "3.3-V LVTTL" -to row_out[2]\nset_instance_assignment -name IO_STANDARD "3.3-V LVTTL" -to row_out[1]\nset_instance_assignment -name IO_STANDARD "3.3-V LVTTL" -to row_out[0]\n\n# keypad scan column: col[3:0]\uff08input with internal pull-high\uff09\nset_location_assignment PIN_AB8 -to col[3]\nset_location_assignment PIN_AB7 -to col[2]\nset_location_assignment PIN_AB6 -to col[1]\nset_location_assignment PIN_AB5 -to col[0]\nset_instance_assignment -name IO_STANDARD "3.3-V LVTTL" -to col[3]\nset_instance_assignment -name IO_STANDARD "3.3-V LVTTL" -to col[2]\nset_instance_assignment -name IO_STANDARD "3.3-V LVTTL" -to col[1]\nset_instance_assignment -name IO_STANDARD "3.3-V LVTTL" -to col[0]\nset_instance_assignment -name WEAK_PULL_UP_RESISTOR ON -to col[3]\nset_instance_assignment -name WEAK_PULL_UP_RESISTOR ON -to col[2]\nset_instance_assignment -name WEAK_PULL_UP_RESISTOR ON -to col[1]\nset_instance_assignment -name WEAK_PULL_UP_RESISTOR ON -to col[0]\n\n#### key value output for keyboard\n# io[8]\u2013io[11] as keycode\uff084-bit\uff09\nset_instance_assignment -name IO_STANDARD "3.3-V LVTTL" -to io[8]\nset_instance_assignment -name IO_STANDARD "3.3-V LVTTL" -to io[9]\nset_instance_assignment -name IO_STANDARD "3.3-V LVTTL" -to io[10]\nset_instance_assignment -name IO_STANDARD "3.3-V LVTTL" -to io[11]\nset_location_assignment PIN_A11 -to io[8]\nset_location_assignment PIN_B11 -to io[9]\nset_location_assignment PIN_D13 -to io[10]\nset_location_assignment PIN_C13 -to io[11]\n\n# io[12] as key_valid\nset_instance_assignment -name IO_STANDARD "3.3-V LVTTL" -to io[12]\nset_location_assignment PIN_E14 -to io[12]\n\n===========================================================================\n### debug LEDS\n# LEDR[0]\u2013LEDR[9] IO_STANDARD & PIN assignment\nset_instance_assignment -name IO_STANDARD "3.3-V LVTTL" -to LEDR[0]\nset_instance_assignment -name IO_STANDARD "3.3-V LVTTL" -to LEDR[1]\nset_instance_assignment -name IO_STANDARD "3.3-V LVTTL" -to LEDR[2]\nset_instance_assignment -name IO_STANDARD "3.3-V LVTTL" -to LEDR[3]\nset_instance_assignment -name IO_STANDARD "3.3-V LVTTL" -to LEDR[4]\nset_instance_assignment -name IO_STANDARD "3.3-V LVTTL" -to LEDR[5]\nset_instance_assignment -name IO_STANDARD "3.3-V LVTTL" -to LEDR[6]\nset_instance_assignment -name IO_STANDARD "3.3-V LVTTL" -to LEDR[7]\nset_instance_assignment -name IO_STANDARD "3.3-V LVTTL" -to LEDR[8]\nset_instance_assignment -name IO_STANDARD "3.3-V LVTTL" -to LEDR[9]\nset_location_assignment PIN_A8 -to LEDR[0]\nset_location_assignment PIN_A9 -to LEDR[1]\nset_location_assignment PIN_A10 -to LEDR[2]\nset_location_assignment PIN_B10 -to LEDR[3]\nset_location_assignment PIN_D13 -to LEDR[4]\nset_location_assignment PIN_C13 -to LEDR[5]\nset_location_assignment PIN_E14 -to LEDR[6]\nset_location_assignment PIN_D14 -to LEDR[7]\nset_location_assignment PIN_A11 -to LEDR[8]\nset_location_assignment PIN_B11 -to LEDR[9]<\/code><\/pre>\n
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