keyboard.md

Keyboard

The keyboard device listens for user keypresses and then sends them to the processor for further handling.

Layout

The physical layout is modern, especially when compared with typical computers of the era where it often seemed as every computer had a different location for various symbols. Retroputer does have a few custom keys, but nothing that would be surprising to modern users.

Retroputer Key	macOS	Windows
fn	Cmd	Windows
gr	Opt	Alt
ctrl	Ctrl	Ctrl
bksp	Delete	Backspace
enter	Return	Enter
caps	Caps Lock	Caps Lock

Logically the keyboard is laid out in five rows of two quadrants. Each quadrant is represented by an I/O byte and can represent if a key is pressed by setting a bit (or a key is not pressed by clearing the bit).

This makes it possible to detect if multiple keys are currently being pressed.

The [GR] Key

The GR key enables you to type graphical characters with the keyboard. You can access an alternate set by pressing GR+SHIFT at the same time.

The [CTRL] Key

The CTRL key is used to translate keys to their corresponding control codes. This only works for alphabetical keys and a few numerical keys. CTRL+H will generate RetSCII code 08, which corresponds to BACKSPACE.

The following maps the CTRL combination to the resulting control code.

CTRL +	RetSCII Code	Control Code
A	01	N/A
B	02	N/A
C	03	Break
D	04	N/A
E	05	N/A
F	06	N/A
G	07	Bell
H	08	Backspace
I	09	Tab
J	0A	Line Feed
K	0B	N/A
L	0C	Form Feed / Clear Screen
M	0D	Carriage Return / Enter
N	0E	N/A
O	0F	N/A
P	10	Cursor Right
Q	11	Cursor Left
R	12	F1
S	13	F2
T	14	F3
U	15	F4
V	16	F5
W	17	F6
X	18	F7
Y	19	F8
Z	1A	F9
0	1B	F10
1	1C	N/A
2	1D	Delete
3	1E	Cursor Up
4	1F	Cursor Down

### The Buffer

Because it's possible that the computer won't have a chance to check for a keyboard character being registered during long computations, the keyboard has a 256-character buffer that will store these until they are read back. Once the user reaches the end of the buffer, additional key presses are lost.

Ports

Port	Name	Notes
0x30	RetSCII code of key pressed	0x00 if no key pressed. Reading will clear the value.
0x31	Buffer Remaining	# of characters remaining in the buffer
0x32	r0:0-7 keys pressed	A set bit indicates the key is currently pressed. Zero indicates that it is up.
0x33	r0:8-F keys pressed
0x34	r1:0-7 keys pressed
0x35	r1:8-F keys pressed
0x36	r2:0-7 keys pressed
0x37	r2:8-F keys pressed
0x38	r3:0-7 keys pressed
0x39	r3:8-F keys pressed
0x3A	r4:0-7 keys pressed
0x3B	r4:8-F keys pressed
0x3C	–
0x3D	–
0x3E	–
0x3F	–

Polling the keyboard

You can poll the keyboard for input as follows:

• Read the value of port 0x30
• If it is non-zero, a key is in the buffer waiting to be processed
  • You must immediately handle the key; checking the buffer will remove the key from the buffer.
• Repeat!
  • Call PUT_CHAR if you'd like to echo the results on screen.

.segment code 0x02000 {
.const PUT_CHAR 0x0FE0C

top:
    do {
        in dl, 0x30
        cmp dl, 0
    } while z
    call [PUT_CHAR]
    br top
}