1. COMP541 Input Devices: Keyboards, Mice and Joysticks
Montek Singh
Sep 22, 2017

2. USB keyboard plugs into the USB port on Nexys 4 boards
Keyboard Interface
USB keyboard plugs into the USB port on Nexys 4 boards

3. USB to PS/2 emulation Host controller on Nexys boards
talks to USB keyboard on one side
speaks PS/2 protocol to the FPGA on the other side
PS/2 used to be the dominant keyboard protocol
PS/2 = a synchronous serial protocol
What does that mean?
Each symbol is transmitted bit-by-bit
8 data bits + 3 control bits
synchronized to the keyboard’s clock (slow)

4. Physical Interface Two lines Read: Clock (15-20KHz) Data
Normally high, asserted low
Read:
pg of Nexys 4 manual
pg of Nexys 4 DDR manual

5. Protocol Bidirectional Assert low For your lab:
Kybd-to-host and host-to-kybd on same wires
CAPS LOCK light for example
Assert low
To send, keyboard starts clocking
sends successive bit on positive edge of clock
host reads bits on negative edges of clock
For your lab:
You shouldn’t need to send anything to keyboard

6. Protocol 11 bits Clocked by keyboard a start bit: always 0
8 bits of data
lsb first
one parity bit (odd)
a stop bit: always 1
Clocked by keyboard
Value should be latched by FPGA on neg edge of keyboard clock
Illustration from

7. What is Sent ASCII is not sent! Scan codes for keys
Most keys have an 8-bit (single byte) scancode
Some have two bytes
A few have even more!
Most (not all, be careful!) keyboards use these scancodes:
Our keyboards have slightly different scan codes! Check before using!
Illustration from Nexys 4 manual

8. Scan Codes Normally translated by software Software takes care of
You remap your keys, for example
Software takes care of
Shift, caps lock, control

9. Some Scan Codes Long Two code sequence common
Some special keys use even more…
…have a look at Break key!

10. Even More Complicated Scan code generated when you press
And when you release
Extra byte: F0 followed by key scan code
Example:
Space pressed, 29 sent
Space released, F0 29 sent

11. Resources Information Scan codes Available on the class website:
Scan codes
Available on the class website:
my Verilog for keyboard
keyboard.sv: keyboard controller hardware
keyboard_test.sv: demo with keyboard and 7-seg display
displays the scan code of the last event from keyboard

12. My Verilog Have Verilog for keyboard To use:
a test/demo which displays data from keyboard onto 7-segment display
have tested it with the FPGA kit; seems to work fine
To use:
You will memory-map the character code register
give the keyboard a memory address so the CPU can read it using lw instructions
Handle presses and releases appropriately in software
Either: Check for a key release before reading a new key press
OR: Delaying next key read (by, say, 1/4th sec)
gives you automatic “key repeat” feature!

13. Mice

14. Mouse Very similar interface (clk & data) Read Verilog
But: 3 words sent w/ mouse movement or button press
Read
pp of Nexys 4 manual
Verilog
I can guide you to modify keyboard.sv to read 3 bytes

15. Movement Movement is relative XS, YS are sign (+ is up/right)
XY, YY are overflow (too fast)
L, R are buttons

16. Scroll Wheel, etc. Extensions to original 2 button PS/2 mouse
See

17. Accelerometer Nexys 4 boards have built-in accelerometer
Verilog module is available on the course website

18. Verilog for accelerometer
module accelerometer(
input wire clk, //use 100MHz clock
//Accelerometer signals
output wire aclSCK,
output wire aclMOSI,
input wire aclMISO,
output wire aclSS,
//Accelerometer data
output wire [8:0] accelX, accelY, // X and Y tilt values
output wire [11:0] accelTmp // temperature sensor value );
AccelerometerCtl accel(clk, 0, aclSCK, aclMOSI, aclMISO, aclSS,
accelX, accelY, accelTmp);
endmodule

19. Built-In Audio Amplifier
Nexys 4 has mono amplifier built-in

20. Built-In Mono Amplifier
Mono output
headphone jack compatible
Very very low-level…!
expects analog waveform on input!
your design on FPGA will have to generate an analog value by rapidly toggling between 0 and 1
e.g., 60% of the time ‘1’ value will approximate an analog value of 0.60V (if range is 0-1V)
Verilog code: available on course website
simple tone generator:
doesn’t use PWM
simply approximates sine wave using square wave
input is period in units of 10 ns (i.e., 100 MHz clock)