Peripherals - High Performance Embedded Systems Design - Lecture Slides, Slides of Computer Science

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4-Integrating Peripherals in

Embedded Systems (cont.)

Using LEDs and switches

• The DE2 board provides four pushbutton switches. Each of

these switches is debounced using a Schmitt Trigger circuit.

• The four outputs called KEY0 , …, KEY3 are connected

directly to the Cyclone II FPGA.

• Each switch provides a high logic level (3.3 volts) when it is

not pressed, and provides a low logic level (0 volts) when

• depressed.

• Since the pushbutton switches are debounced, they are

appropriate for use as clock or reset inputs in a circuit.

Using LEDs and switches

Using LEDs and switches

There are also 18 toggle switches (sliders) on the DE2 board.

These switches are not debounced, and are intended for use

as level-sensitive data inputs to a circuit.

When a switch is in the DOWN position (closest to the edge

of the board) it provides a low logic level (0 volts) to the

FPGA, and when the switch is in the UP position it provides a

high logic level (3.3 volts).

Using LEDs and switches

• There are 27 user-controllable LEDs on the DE2 board.

• Eighteen red LEDs are situated above the 18 toggle

switches

• Eight green LEDs are found above the pushbutton switches

(the 9th green LED is in the middle of the 7-segment

displays).

• Each LED is driven directly by a pin on the

• Cyclone II FPGA; driving its associated pin to a high logic

level turns the LED on, and driving the

• pin low turns it off.

Using LEDs and switches

Seven Segment Display

• The DE2 Board has eight 7-segment

displays. These displays are arranged into

two pairs and a group of four, with the intent

of displaying numbers of various sizes.

• Applying a low logic level to a segment

causes it to light up, and applying a high

logic level turns it off.

LED_pio.v

module led_red ( // inputs: address, chipselect, clk, reset_n, write_n, writedata, // outputs: out_port ); output [ 17: 0] out_port; input [ 1: 0] address; input chipselect; input clk; input reset_n; input write_n; input [ 17: 0] writedata; wire clk_en; reg [ 17: 0] data_out; wire [ 17: 0] out_port; assign clk_en = 1; always @(posedge clk or negedge reset_n) begin if (reset_n == 0) data_out <= 0; else if (chipselect && ~write_n && (address == 0)) data_out <= writedata[17 : 0]; end assign out_port = data_out; endmodule

Button_pio.v (1)

module button_pio ( // inputs: address, chipselect, clk, in_port, reset_n, write_n, writedata, // outputs: irq, readdata ); output irq; output [ 3: 0] readdata; input [ 1: 0] address; input chipselect; input clk; input [ 3: 0] in_port; input reset_n; input write_n; input [ 3: 0] writedata; wire clk_en; reg [ 3: 0] d1_data_in; reg [ 3: 0] d2_data_in; wire [ 3: 0] data_in; reg [ 3: 0] edge_capture; wire edge_capture_wr_strobe; wire [ 3: 0] edge_detect; wire irq; reg [ 3: 0] irq_mask; wire [ 3: 0] read_mux_out; reg [ 3: 0] readdata; assign clk_en = 1;

Button_pio.v (2)

• assign read_mux_out = ({4 {(address == 0)}} & data_in) |
• ({4 {(address == 2)}} & irq_mask) |
• ({4 {(address == 3)}} & edge_capture);
• always @(posedge clk or negedge reset_n)
• begin
• if (reset_n == 0)
• readdata <= 0;
• else if (clk_en)
• readdata <= read_mux_out;
• end
• assign data_in = in_port;
• always @(posedge clk or negedge reset_n)
• begin
• if (reset_n == 0)
• irq_mask <= 0;
• else if (chipselect && ~write_n && (address == 2))
• irq_mask <= writedata[3 : 0];
• end
• assign irq = |(edge_capture & irq_mask);
• assign edge_capture_wr_strobe = chipselect && ~write_n && (address == 3);
• always @(posedge clk or negedge reset_n)
• begin
• if (reset_n == 0)
• edge_capture[0] <= 0;
• else if (clk_en)
• if (edge_capture_wr_strobe)
• edge_capture[0] <= 0;
• else if (edge_detect[0])
• edge_capture[0] <= -1;
• end

Seven Segment Display: Pin assignment

Shown above the pin assignments for segment digit 0 only

Seven Segment Display: Pin assignment

Seven segment

• module SEG7_LUT ( oSEG,iDIG );
• input [3:0] iDIG;
• output [6:0] oSEG;
• reg [6:0] oSEG;
• always @(iDIG)
• begin
• case(iDIG)
• 4'h1: oSEG = 7'b1111001; // ---t----
• 4'h2: oSEG = 7'b0100100; // | |
• 4'h3: oSEG = 7'b0110000; // lt rt
• 4'h4: oSEG = 7'b0011001; // | |
• 4'h5: oSEG = 7'b0010010; // ---m----
• 4'h6: oSEG = 7'b0000010; // | |
• 4'h7: oSEG = 7'b1111000; // lb rb
• 4'h8: oSEG = 7'b0000000; // | |
• 4'h9: oSEG = 7'b0011000; // ---b----
• 4'ha: oSEG = 7'b0001000;
• 4'hb: oSEG = 7'b0000011;
• 4'hc: oSEG = 7'b1000110;
• 4'hd: oSEG = 7'b0100001;
• 4'he: oSEG = 7'b0000110;
• 4'hf: oSEG = 7'b0001110;
• 4'h0: oSEG = 7'b1000000;
• endcase
• end
• endmodule

LCD controller

E

R/W

RS

DB7–DB

LCD

controller

communications

bus

microcontroller

void WriteChar(char c){ RS = 1; /* indicate data being sent / DATA_BUS = c; / send data to LCD / EnableLCD(45); / toggle the LCD Enable with delay of 45 units of time*/ }

CODES

I/D = 1 cursor moves left DL = 1 8-bit

I/D = 0 cursor moves right DL = 0 4-bit

S = 1 with display shift N = 1 2 rows

S/C =1 display shift N = 0 1 row

S/C = 0 cursor movement F = 1 5x10 dots

R/L = 1 shift to right F = 0 5x7 dots

R/L = 0 shift to left

RS R/W DB 7 DB 6 DB 5 DB 4 DB 3 DB 2 DB 1 DB 0 Description

0 0 0 0 0 0 0 0 0 1 Clears all display, return cursor home

0 0 0 0 0 0 0 0 1 * Returns cursor home

0 0 0 0 0 0 0 1 I/D S Sets cursor move direction and/orspecifies not to shift display

0 0 0 0 0 0 1 D C B ON/OFF of all display(D), cursorON/OFF (C), and blink position (B)

0 0 0 0 0 1 S/C R/L * * Move cursor and shifts display

0 0 0 0 1 DL N F * * Sets interface data length, number ofdisplay lines, and character font

1 0 WRITE DATA Writes Data