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//------------------------------------------------------------------------------------- // // Author: John Clayton // Date : April 30, 2001 // Update: 4/30/01 copied this file from lcd_2.v (pared down). // Update: 5/24/01 changed the first module from "ps2_keyboard_receiver" // to "ps2_keyboard_interface" // Update: 5/29/01 Added input synchronizing flip-flops. Changed state // encoding (m1) for good operation after part config. // Update: 5/31/01 Added low drive strength and slow transitions to ps2_clk // and ps2_data in the constraints file. Added the signal // "tx_shifting_done" as distinguished from "rx_shifting_done." // Debugged the transmitter portion in the lab. // Update: 6/01/01 Added horizontal tab to the ascii output. // Update: 6/01/01 Added parameter TRAP_SHIFT_KEYS. // Update: 6/05/01 Debugged the "debounce" timer functionality. // Used 60usec timer as a "watchdog" timeout during // receive from the keyboard. This means that a keyboard // can now be "hot plugged" into the interface, without // messing up the bit_count, since the bit_count is reset // to zero during periods of inactivity anyway. This was // difficult to debug. I ended up using the logic analyzer, // and had to scratch my head quite a bit. // Update: 6/06/01 Removed extra comments before the input synchronizing // flip-flops. Used the correct parameter to size the // 5usec_timer_count. Changed the name of this file from // ps2.v to ps2_keyboard.v // Update: 6/06/01 Removed "&& q[7:0]" in output_strobe logic. Removed extra // commented out "else" condition in the shift register and // bit counter. // Update: 6/07/01 Changed default values for 60usec timer parameters so that // they correspond to 60usec for a 49.152MHz clock. // // // // // // Description //------------------------------------------------------------------------------------- // This is a state-machine driven serial-to-parallel and parallel-to-serial // interface to the ps2 style keyboard interface. The details of the operation // of the keyboard interface were obtained from the following website: // // http://www.beyondlogic.org/keyboard/keybrd.htm // // Some aspects of the keyboard interface are not implemented (e.g, parity // checking for the receive side, and recognition of the various commands // which the keyboard sends out, such as "power on selt test passed," "Error" // and "Resend.") However, if the user wishes to recognize these reply // messages, the scan code output can always be used to extend functionality // as desired. // // Note that the "Extended" (0xE0) and "Released" (0xF0) codes are recognized. // The rx interface provides separate indicator flags for these two conditions // with every valid character scan code which it provides. The shift keys are // also trapped by the interface, in order to provide correct uppercase ASCII // characters at the ascii output, although the scan codes for the shift keys // are still provided at the scan code output. So, the left/right ALT keys // can be differentiated by the presence of the rx_entended signal, while the // left/right shift keys are differentiable by the different scan codes // received. // // The interface to the ps2 keyboard uses ps2_clk clock rates of // 30-40 kHz, dependent upon the keyboard itself. The rate at which the state // machine runs should be at least twice the rate of the ps2_clk, so that the // states can accurately follow the clock signal itself. Four times // oversampling is better. Say 200kHz at least. The upper limit for clocking // the state machine will undoubtedly be determined by delays in the logic // which decodes the scan codes into ASCII equivalents. The maximum speed // will be most likely many megahertz, depending upon target technology. // In order to run the state machine extremely fast, synchronizing flip-flops // have been added to the ps2_clk and ps2_data inputs of the state machine. // This avoids poor performance related to slow transitions of the inputs. // // Because this is a bi-directional interface, while reading from the keyboard // the ps2_clk and ps2_data lines are used as inputs. While writing to the // keyboard, however (which may be done at any time. If writing interrupts a // read from the keyboard, the keyboard will buffer up its data, and send // it later) both the ps2_clk and ps2_data lines are occasionally pulled low, // and pullup resistors are used to bring the lines high again, by setting // the drivers to high impedance state. // // The tx interface, for writing to the keyboard, does not provide any special // pre-processing. It simply transmits the 8-bit command value to the // keyboard. // // Pullups MUST BE USED on the ps2_clk and ps2_data lines for this design, // whether they be internal to an FPGA I/O pad, or externally placed. // If internal pullups are used, they may be fairly weak, causing bounces // due to crosstalk, etc. There is a "debounce timer" implemented in order // to eliminate erroneous state transitions which would occur based on bounce. // // Parameters are provided in order to configure and appropriately size the // counter of a 60 microsecond timer used in the transmitter, depending on // the clock frequency used. The 60 microsecond period is guaranteed to be // more than one period of the ps2_clk_s signal. // // Also, a smaller 5 microsecond timer has been included for "debounce". // This is used because, with internal pullups on the ps2_clk and ps2_data // lines, there is some bouncing around which occurs // // A parameter TRAP_SHIFT_KEYS allows the user to eliminate shift keypresses // from producing scan codes (along with their "undefined" ASCII equivalents) // at the output of the interface. If TRAP_SHIFT_KEYS is non-zero, the shift // key status will only be reported by rx_shift_key_on. No ascii or scan // codes will be reported for the shift keys. This is useful for those who // wish to use the ASCII data stream, and who don't want to have to "filter // out" the shift key codes. // //------------------------------------------------------------------------------------- `resetall `timescale 1ns/100ps `define TOTAL_BITS 11 `define EXTEND_CODE 16'hE0 `define RELEASE_CODE 16'hF0 `define LEFT_SHIFT 16'h12 `define RIGHT_SHIFT 16'h59 module ps2_keyboard_interface ( clk, reset, ps2_clk, ps2_data, rx_extended, rx_released, rx_shift_key_on, rx_scan_code, rx_ascii, rx_data_ready, // rx_read_o rx_read, // rx_read_ack_i tx_data, tx_write, tx_write_ack_o, tx_error_no_keyboard_ack ); // Parameters // The timer value can be up to (2^bits) inclusive. parameter TIMER_60USEC_VALUE_PP = 2950; // Number of sys_clks for 60usec. parameter TIMER_60USEC_BITS_PP = 12; // Number of bits needed for timer parameter TIMER_5USEC_VALUE_PP = 186; // Number of sys_clks for debounce parameter TIMER_5USEC_BITS_PP = 8; // Number of bits needed for timer parameter TRAP_SHIFT_KEYS_PP = 0; // Default: No shift key trap. // State encodings, provided as parameters // for flexibility to the one instantiating the module. // In general, the default values need not be changed. // State "m1_rx_clk_l" has been chosen on purpose. Since the input // synchronizing flip-flops initially contain zero, it takes one clk // for them to update to reflect the actual (idle = high) status of // the I/O lines from the keyboard. Therefore, choosing 0 for m1_rx_clk_l // allows the state machine to transition to m1_rx_clk_h when the true // values of the input signals become present at the outputs of the // synchronizing flip-flops. This initial transition is harmless, and it // eliminates the need for a "reset" pulse before the interface can operate. parameter m1_rx_clk_h = 1; parameter m1_rx_clk_l = 0; parameter m1_rx_falling_edge_marker = 13; parameter m1_rx_rising_edge_marker = 14; parameter m1_tx_force_clk_l = 3; parameter m1_tx_first_wait_clk_h = 10; parameter m1_tx_first_wait_clk_l = 11; parameter m1_tx_reset_timer = 12; parameter m1_tx_wait_clk_h = 2; parameter m1_tx_clk_h = 4; parameter m1_tx_clk_l = 5; parameter m1_tx_wait_keyboard_ack = 6; parameter m1_tx_done_recovery = 7; parameter m1_tx_error_no_keyboard_ack = 8; parameter m1_tx_rising_edge_marker = 9; parameter m2_rx_data_ready = 1; parameter m2_rx_data_ready_ack = 0; // I/O declarations input clk; input reset; inout ps2_clk; inout ps2_data; output rx_extended; output rx_released; output rx_shift_key_on; output [7:0] rx_scan_code; output [7:0] rx_ascii; output rx_data_ready; input rx_read; input [7:0] tx_data; input tx_write; output tx_write_ack_o; output tx_error_no_keyboard_ack; reg rx_extended; reg rx_released; reg [7:0] rx_scan_code; reg [7:0] rx_ascii; reg rx_data_ready; reg tx_error_no_keyboard_ack; // Internal signal declarations wire timer_60usec_done; wire timer_5usec_done; wire extended; wire released; wire shift_key_on; // NOTE: These two signals used to be one. They // were split into two signals because of // shift key trapping. With shift key // trapping, no event is generated externally, // but the "hold" data must still be cleared // anyway regardless, in preparation for the // next scan codes. wire rx_output_event; // Used only to clear: hold_released, hold_extended wire rx_output_strobe; // Used to produce the actual output. wire tx_parity_bit; wire rx_shifting_done; wire tx_shifting_done; wire [11:0] shift_key_plus_code; reg [`TOTAL_BITS-1:0] q; reg [3:0] m1_state; reg [3:0] m1_next_state; reg m2_state; reg m2_next_state; reg [3:0] bit_count; reg enable_timer_60usec; reg enable_timer_5usec; reg [TIMER_60USEC_BITS_PP-1:0] timer_60usec_count; reg [TIMER_5USEC_BITS_PP-1:0] timer_5usec_count; reg [7:0] ascii; // "REG" type only because a case statement is used. reg left_shift_key; reg right_shift_key; reg hold_extended; // Holds prior value, cleared at rx_output_strobe reg hold_released; // Holds prior value, cleared at rx_output_strobe reg ps2_clk_s; // Synchronous version of this input reg ps2_data_s; // Synchronous version of this input reg ps2_clk_hi_z; // Without keyboard, high Z equals 1 due to pullups. reg ps2_data_hi_z; // Without keyboard, high Z equals 1 due to pullups. //-------------------------------------------------------------------------- // Module code assign ps2_clk = ps2_clk_hi_z?1'bZ:1'b0; assign ps2_data = ps2_data_hi_z?1'bZ:1'b0; // Input "synchronizing" logic -- synchronizes the inputs to the state // machine clock, thus avoiding errors related to // spurious state machine transitions. always @(posedge clk) begin ps2_clk_s <= ps2_clk; ps2_data_s <= ps2_data; end // State register always @(posedge clk) begin : m1_state_register if (reset) m1_state <= m1_rx_clk_h; else m1_state <= m1_next_state; end // State transition logic always @(m1_state or q or tx_shifting_done or tx_write or ps2_clk_s or ps2_data_s or timer_60usec_done or timer_5usec_done ) begin : m1_state_logic // Output signals default to this value, unless changed in a state condition. ps2_clk_hi_z <= 1; ps2_data_hi_z <= 1; tx_error_no_keyboard_ack <= 0; enable_timer_60usec <= 0; enable_timer_5usec <= 0; case (m1_state) m1_rx_clk_h : begin enable_timer_60usec <= 1; if (tx_write) m1_next_state <= m1_tx_reset_timer; else if (~ps2_clk_s) m1_next_state <= m1_rx_falling_edge_marker; else m1_next_state <= m1_rx_clk_h; end m1_rx_falling_edge_marker : begin enable_timer_60usec <= 0; m1_next_state <= m1_rx_clk_l; end m1_rx_rising_edge_marker : begin enable_timer_60usec <= 0; m1_next_state <= m1_rx_clk_h; end m1_rx_clk_l : begin enable_timer_60usec <= 1; if (tx_write) m1_next_state <= m1_tx_reset_timer; else if (ps2_clk_s) m1_next_state <= m1_rx_rising_edge_marker; else m1_next_state <= m1_rx_clk_l; end m1_tx_reset_timer: begin enable_timer_60usec <= 0; m1_next_state <= m1_tx_force_clk_l; end m1_tx_force_clk_l : begin enable_timer_60usec <= 1; ps2_clk_hi_z <= 0; // Force the ps2_clk line low. if (timer_60usec_done) m1_next_state <= m1_tx_first_wait_clk_h; else m1_next_state <= m1_tx_force_clk_l; end m1_tx_first_wait_clk_h : begin enable_timer_5usec <= 1; ps2_data_hi_z <= 0; // Start bit. if (~ps2_clk_s && timer_5usec_done) m1_next_state <= m1_tx_clk_l; else m1_next_state <= m1_tx_first_wait_clk_h; end // This state must be included because the device might possibly // delay for up to 10 milliseconds before beginning its clock pulses. // During that waiting time, we cannot drive the data (q[0]) because it // is possibly 1, which would cause the keyboard to abort its receive // and the expected clocks would then never be generated. m1_tx_first_wait_clk_l : begin ps2_data_hi_z <= 0; if (~ps2_clk_s) m1_next_state <= m1_tx_clk_l; else m1_next_state <= m1_tx_first_wait_clk_l; end m1_tx_wait_clk_h : begin enable_timer_5usec <= 1; ps2_data_hi_z <= q[0]; if (ps2_clk_s && timer_5usec_done) m1_next_state <= m1_tx_rising_edge_marker; else m1_next_state <= m1_tx_wait_clk_h; end m1_tx_rising_edge_marker : begin ps2_data_hi_z <= q[0]; m1_next_state <= m1_tx_clk_h; end m1_tx_clk_h : begin ps2_data_hi_z <= q[0]; if (tx_shifting_done) m1_next_state <= m1_tx_wait_keyboard_ack; else if (~ps2_clk_s) m1_next_state <= m1_tx_clk_l; else m1_next_state <= m1_tx_clk_h; end m1_tx_clk_l : begin ps2_data_hi_z <= q[0]; if (ps2_clk_s) m1_next_state <= m1_tx_wait_clk_h; else m1_next_state <= m1_tx_clk_l; end m1_tx_wait_keyboard_ack : begin if (~ps2_clk_s && ps2_data_s) m1_next_state <= m1_tx_error_no_keyboard_ack; else if (~ps2_clk_s && ~ps2_data_s) m1_next_state <= m1_tx_done_recovery; else m1_next_state <= m1_tx_wait_keyboard_ack; end m1_tx_done_recovery : begin if (ps2_clk_s && ps2_data_s) m1_next_state <= m1_rx_clk_h; else m1_next_state <= m1_tx_done_recovery; end m1_tx_error_no_keyboard_ack : begin tx_error_no_keyboard_ack <= 1; if (ps2_clk_s && ps2_data_s) m1_next_state <= m1_rx_clk_h; else m1_next_state <= m1_tx_error_no_keyboard_ack; end default : m1_next_state <= m1_rx_clk_h; endcase end // State register always @(posedge clk) begin : m2_state_register if (reset) m2_state <= m2_rx_data_ready_ack; else m2_state <= m2_next_state; end // State transition logic always @(m2_state or rx_output_strobe or rx_read) begin : m2_state_logic case (m2_state) m2_rx_data_ready_ack: begin rx_data_ready <= 1'b0; if (rx_output_strobe) m2_next_state <= m2_rx_data_ready; else m2_next_state <= m2_rx_data_ready_ack; end m2_rx_data_ready: begin rx_data_ready <= 1'b1; if (rx_read) m2_next_state <= m2_rx_data_ready_ack; else m2_next_state <= m2_rx_data_ready; end default : m2_next_state <= m2_rx_data_ready_ack; endcase end // This is the bit counter always @(posedge clk) begin if ( reset || rx_shifting_done || (m1_state == m1_tx_wait_keyboard_ack) // After tx is done. ) bit_count <= 0; // normal reset else if (timer_60usec_done && (m1_state == m1_rx_clk_h) && (ps2_clk_s) ) bit_count <= 0; // rx watchdog timer reset else if ( (m1_state == m1_rx_falling_edge_marker) // increment for rx ||(m1_state == m1_tx_rising_edge_marker) // increment for tx ) bit_count <= bit_count + 1; end // This signal is high for one clock at the end of the timer count. assign rx_shifting_done = (bit_count == `TOTAL_BITS); assign tx_shifting_done = (bit_count == `TOTAL_BITS-1); // This is the signal which enables loading of the shift register. // It also indicates "ack" to the device writing to the transmitter. assign tx_write_ack_o = ( (tx_write && (m1_state == m1_rx_clk_h)) ||(tx_write && (m1_state == m1_rx_clk_l)) ); // This is the ODD parity bit for the transmitted word. assign tx_parity_bit = ~^tx_data; // This is the shift register always @(posedge clk) begin if (reset) q <= 0; else if (tx_write_ack_o) q <= {1'b1,tx_parity_bit,tx_data,1'b0}; else if ( (m1_state == m1_rx_falling_edge_marker) ||(m1_state == m1_tx_rising_edge_marker) ) q <= {ps2_data_s,q[`TOTAL_BITS-1:1]}; end // This is the 60usec timer counter always @(posedge clk) begin if (~enable_timer_60usec) timer_60usec_count <= 0; else if (~timer_60usec_done) timer_60usec_count <= timer_60usec_count + 1; end assign timer_60usec_done = (timer_60usec_count == (TIMER_60USEC_VALUE_PP - 1)); // This is the 5usec timer counter always @(posedge clk) begin if (~enable_timer_5usec) timer_5usec_count <= 0; else if (~timer_5usec_done) timer_5usec_count <= timer_5usec_count + 1; end assign timer_5usec_done = (timer_5usec_count == TIMER_5USEC_VALUE_PP - 1); // Create the signals which indicate special scan codes received. // These are the "unlatched versions." assign extended = (q[8:1] == `EXTEND_CODE) && rx_shifting_done; assign released = (q[8:1] == `RELEASE_CODE) && rx_shifting_done; // Store the special scan code status bits // Not the final output, but an intermediate storage place, // until the entire set of output data can be assembled. always @(posedge clk) begin if (reset || rx_output_event) begin hold_extended <= 0; hold_released <= 0; end else begin if (rx_shifting_done && extended) hold_extended <= 1; if (rx_shifting_done && released) hold_released <= 1; end end // These bits contain the status of the two shift keys always @(posedge clk) begin if (reset) left_shift_key <= 0; else if ((q[8:1] == `LEFT_SHIFT) && rx_shifting_done && ~hold_released) left_shift_key <= 1; else if ((q[8:1] == `LEFT_SHIFT) && rx_shifting_done && hold_released) left_shift_key <= 0; end always @(posedge clk) begin if (reset) right_shift_key <= 0; else if ((q[8:1] == `RIGHT_SHIFT) && rx_shifting_done && ~hold_released) right_shift_key <= 1; else if ((q[8:1] == `RIGHT_SHIFT) && rx_shifting_done && hold_released) right_shift_key <= 0; end assign rx_shift_key_on = left_shift_key || right_shift_key; // Output the special scan code flags, the scan code and the ascii always @(posedge clk) begin if (reset) begin rx_extended <= 0; rx_released <= 0; rx_scan_code <= 0; rx_ascii <= 0; end else if (rx_output_strobe) begin rx_extended <= hold_extended; rx_released <= hold_released; rx_scan_code <= q[8:1]; rx_ascii <= ascii; end end // Store the final rx output data only when all extend and release codes // are received and the next (actual key) scan code is also ready. // (the presence of rx_extended or rx_released refers to the // the current latest scan code received, not the previously latched flags.) assign rx_output_event = (rx_shifting_done && ~extended && ~released ); assign rx_output_strobe = (rx_shifting_done && ~extended && ~released && ( (TRAP_SHIFT_KEYS_PP == 0) || ( (q[8:1] != `RIGHT_SHIFT) &&(q[8:1] != `LEFT_SHIFT) ) ) ); // This part translates the scan code into an ASCII value... // Only the ASCII codes which I considered important have been included. // if you want more, just add the appropriate case statement lines... // (You will need to know the keyboard scan codes you wish to assign.) // The entries are listed in ascending order of ASCII value. assign shift_key_plus_code = {3'b0,rx_shift_key_on,q[8:1]}; always @(shift_key_plus_code) begin casez (shift_key_plus_code) 12'h?66 : ascii <= 8'h08; // Backspace ("backspace" key) 12'h?0d : ascii <= 8'h09; // Horizontal Tab 12'h?5a : ascii <= 8'h0d; // Carriage return ("enter" key) 12'h?76 : ascii <= 8'h1b; // Escape ("esc" key) 12'h?29 : ascii <= 8'h20; // Space 12'h116 : ascii <= 8'h21; // ! 12'h152 : ascii <= 8'h22; // " 12'h126 : ascii <= 8'h23; // # 12'h125 : ascii <= 8'h24; // $ 12'h12e : ascii <= 8'h25; // % 12'h13d : ascii <= 8'h26; // & 12'h052 : ascii <= 8'h27; // ' 12'h146 : ascii <= 8'h28; // ( 12'h145 : ascii <= 8'h29; // ) 12'h13e : ascii <= 8'h2a; // * 12'h155 : ascii <= 8'h2b; // + 12'h041 : ascii <= 8'h2c; // , 12'h04e : ascii <= 8'h2d; // - 12'h049 : ascii <= 8'h2e; // . 12'h04a : ascii <= 8'h2f; // / 12'h045 : ascii <= 8'h30; // 0 12'h016 : ascii <= 8'h31; // 1 12'h01e : ascii <= 8'h32; // 2 12'h026 : ascii <= 8'h33; // 3 12'h025 : ascii <= 8'h34; // 4 12'h02e : ascii <= 8'h35; // 5 12'h036 : ascii <= 8'h36; // 6 12'h03d : ascii <= 8'h37; // 7 12'h03e : ascii <= 8'h38; // 8 12'h046 : ascii <= 8'h39; // 9 12'h14c : ascii <= 8'h3a; // : 12'h04c : ascii <= 8'h3b; // ; 12'h141 : ascii <= 8'h3c; // < 12'h055 : ascii <= 8'h3d; // = 12'h149 : ascii <= 8'h3e; // > 12'h14a : ascii <= 8'h3f; // ? 12'h11e : ascii <= 8'h40; // @ 12'h11c : ascii <= 8'h41; // A 12'h132 : ascii <= 8'h42; // B 12'h121 : ascii <= 8'h43; // C 12'h123 : ascii <= 8'h44; // D 12'h124 : ascii <= 8'h45; // E 12'h12b : ascii <= 8'h46; // F 12'h134 : ascii <= 8'h47; // G 12'h133 : ascii <= 8'h48; // H 12'h143 : ascii <= 8'h49; // I 12'h13b : ascii <= 8'h4a; // J 12'h142 : ascii <= 8'h4b; // K 12'h14b : ascii <= 8'h4c; // L 12'h13a : ascii <= 8'h4d; // M 12'h131 : ascii <= 8'h4e; // N 12'h144 : ascii <= 8'h4f; // O 12'h14d : ascii <= 8'h50; // P 12'h115 : ascii <= 8'h51; // Q 12'h12d : ascii <= 8'h52; // R 12'h11b : ascii <= 8'h53; // S 12'h12c : ascii <= 8'h54; // T 12'h13c : ascii <= 8'h55; // U 12'h12a : ascii <= 8'h56; // V 12'h11d : ascii <= 8'h57; // W 12'h122 : ascii <= 8'h58; // X 12'h135 : ascii <= 8'h59; // Y 12'h11a : ascii <= 8'h5a; // Z 12'h054 : ascii <= 8'h5b; // [ 12'h05d : ascii <= 8'h5c; // \ 12'h05b : ascii <= 8'h5d; // ] 12'h136 : ascii <= 8'h5e; // ^ 12'h14e : ascii <= 8'h5f; // _ 12'h00e : ascii <= 8'h60; // ` 12'h01c : ascii <= 8'h61; // a 12'h032 : ascii <= 8'h62; // b 12'h021 : ascii <= 8'h63; // c 12'h023 : ascii <= 8'h64; // d 12'h024 : ascii <= 8'h65; // e 12'h02b : ascii <= 8'h66; // f 12'h034 : ascii <= 8'h67; // g 12'h033 : ascii <= 8'h68; // h 12'h043 : ascii <= 8'h69; // i 12'h03b : ascii <= 8'h6a; // j 12'h042 : ascii <= 8'h6b; // k 12'h04b : ascii <= 8'h6c; // l 12'h03a : ascii <= 8'h6d; // m 12'h031 : ascii <= 8'h6e; // n 12'h044 : ascii <= 8'h6f; // o 12'h04d : ascii <= 8'h70; // p 12'h015 : ascii <= 8'h71; // q 12'h02d : ascii <= 8'h72; // r 12'h01b : ascii <= 8'h73; // s 12'h02c : ascii <= 8'h74; // t 12'h03c : ascii <= 8'h75; // u 12'h02a : ascii <= 8'h76; // v 12'h01d : ascii <= 8'h77; // w 12'h022 : ascii <= 8'h78; // x 12'h035 : ascii <= 8'h79; // y 12'h01a : ascii <= 8'h7a; // z 12'h154 : ascii <= 8'h7b; // { 12'h15d : ascii <= 8'h7c; // | 12'h15b : ascii <= 8'h7d; // } 12'h10e : ascii <= 8'h7e; // ~ 12'h?71 : ascii <= 8'h7f; // (Delete OR DEL on numeric keypad) default : ascii <= 8'h2e; // '.' used for unlisted characters. endcase end endmodule //`undefine TOTAL_BITS //`undefine EXTEND_CODE //`undefine RELEASE_CODE //`undefine LEFT_SHIFT //`undefine RIGHT_SHIFT