A PS2 Keyboard Input FPGA Code Example. This
circuit example adds a very basic PS2 Keyboard input port to the
V2 FPGA Prototype board. It assumes the
user is familiar with the very common "PS2 keyboard Interface", most
commonly found in IBM PC's and clones. See
here for more details.
The actual hardware on the board consist of a 2X5 pin connector to a PS2
keyboard socket (via a ribbon cable) at the back of your S100 bus box.
Please note the pinout of this connector is exactly the same pinout as the PS2
connector on our V3 MSDOS
Support Board (Not the V2 MSDOS Board). BTW, this pinout is different from the PS2
pinout on our
Console IO Board. Of course it can be easily changed.
Introduction
In 1987 IBM introduced its PS2 line of PCs. This was an effort to stem the flow
of "IBM PC clones" that were swamping the market. Major changes included
the introduction replacing the ISA bus completely with a "Micro Channel Bus".
This MCA bus was not well received by the PC customer base, since it was
proprietary to IBM and was not commonly implemented by any of the other
PC-compatible makers. Eventually IBM abandoned the architecture and return to
the standard ISA bus. The one and only item PS2 computers offered
that remained , was the keyboard and mouse interface. It went on to
dominate world wide all desktop and laptop interfaces. Today, its
almost impossible to find a new keyboard that does not utilize a PS2 interface
(or its USB adaptor equivalent).
Unlike earlier keyboard interfaces that returned simple parallel 8 bit ASCII
codes from the keyboard, PS2 keyboards return a sophisticated serial code over
two wires (CLK & DATA). Please read
here to understand the
PS2 keyboard protocol if you are not familiar with it.
We will utilize our FPGA Prototype board to examine this PS2 data stream and
display the pressed key ASCII code on the 8 LEDs of our FPGA board.
Again there are many ways this can be done with a Cyclone IV FPGA and the are
numerous examples available on the web.
I found this simple one from DigiKey to be excellent.
PS/2 Keyboard to ASCII Converter (VHDL).
Since we are working with .bdf files we need to convert this .VHD
file to a .bsf
file. We do this from the Quartus File Menu.
Load the ps2_keyboard_to_ascii.vhd
file.
The click File dropdown menu and select "Create/Update".
Then select, Create Symbol Files from the
Current File.
You must have the support files,
ps2_keyboard.vhl and debounce.vhd files in the
current folder as well. (See the bottom of this page for everything that
is needed).
Hooking up the PS2 keyboard on our FPGA board is dirt simple.
Here is the core of the PS2_key.bdf
file.
We connect pins P17 4 & 5 to the PS2 connector at the top of the board.
Load the compiled code into the FPGA. When you press a PS2 keyboard character
the appropriate 8 bit ASCII code should appear on LEDs 0-7. For example
pressing the "1" key should display 31H.
Upon each key press the WaveShare LED2 should flash.
As an FPGA coding exercise you can combine this circuit with PortIN_Test.bdf so that
you can read the keyboard on say port 68H
and the keyboard status on port 69H.
Note this is a very simple example of using our Cyclone IV to for a PS2
keyboard. More elaborate interfaces have a bidirectional interface with the
keyboard.
Please study the files below to understand completely what is going on before
going on to more complicated examples.
Bugs
No bugs noted to date. The PS2 socket will not work with PS2->USB keyboard
adaptors however. You need a true PS2 keyboard or a PC AT keyboard connection.
(This is probably something that could be decoded in the FPGA -- a future
project !).
