Buttons and joystick¶

The leguan provides five push-buttons and a digital joystick:

Important

All the buttons and the joystick signals are active low, meaning that when activating them they will provide a logic level 0, and when they are not activated, they give a logic level 1. Furthermore, some of them have external pull-up resistors, and some of them require an FPGA-IOB pull-up resistor to function correctly!

Buttons¶

The leguan board provides five general purpose buttons. Although the reset button is marked specially, it’s functionality is not different from the other four.

The table below shows the pins on which they are connected on the FPGA, and if they require an FPGA-IOB pull-up resistor:

Name:	FPGA pin:	requires pull-up:
Reset button	PIN_A11	No
Button 1	PIN_T2	No
Button 2	PIN_V3	Yes
Button 3	PIN_T21	No
Button 4	PIN_T1	No

Below you find the snippets on how to use these buttons in your toplevel.

Note

Except from button 2 all are connected to clock-input-pins of the FPGA. They can hence also be used as clock source.

Joystick¶

The table below shows the pins on which the joystick is connected on the FPGA and if the connections requires an FPGA-IOB pull-up resistor:

Name:	FPGA pin:	requires pull-up:
up	PIN_W2	Yes
down	PIN_E9	Yes
left	PIN_W1	Yes
right	PIN_G8	Yes
center	PIN_G11	Yes

Below you find the snippets on how to use these buttons in your toplevel.

Using the buttons and/or joystick¶

In this section you find a VHDL top-level entity and the corresponding tcl-file that you can use to use the button(s) and/or joystick.

Important

Although VHDL is case-insensitive, the tcl-files are not. Meaning that the port-names in the top-level entity need to be copied exactly in the tcl-files.

An example for a VHDL top-level entity is shown below:

library ieee;
use ieee.std_logic_1164.all;

entity leguanToplevel is
  port ( button1_b        : in std_logic;
         joystickCenter_b : in std_logic );
end leguanToplevel;

To connect the above ports to the correct pins of the FPGA, following tcl-script can be used:

set_location_assignment PIN_T2 -to button1_b
set_location_assignment PIN_G11 -to joystickCenter_b

set_instance_assignment -name WEAK_PULL_UP_RESISTOR ON -to joystickCenter_b

Note

The suffix _b to the port names. This is general practice to indicate an active-low signal.
The set_instance_assignment -name WEAK_PULL_UP_RESISTOR ON -to joystickCenter_b line in the tcl-script. This instructs quartus to activate the FPGA pull-up resistor in the IOB. If this line would be omitted, the joystickCenter_b does not function. The reason for this is that in case the center of the joystick is not activated, the input is floating.
As button1_b does not require an FPGA IOB pull-up resistor, you must not specify a set_instance_assignment -name WEAK_PULL_UP_RESISTOR ON .... for this signal in the tcl-file!

Hint

To activate the assignments, following steps need to be taken in quartus:

Go to Tools->Tcl scripts....
Add the tcl script to your project by pressing the Button Add to Project....
Highlight the tcl script by clicking on it in the Libraries: window.
Press the Run button.