Digilent DIO1 - Manual (Page 5)

Digilent DIO1 Reference Manual Digilent, Inc.
www.digilentinc.com page 5 of 10
Copyright Digilent, Inc. All rights reserved. Other product and company names mentioned may be trademarks of their respective owners.
Keyboard
The keyboard uses open collector drivers so
that either the keyboard or an attached host
device can drive the two-wire bus (if the host
device will not send data to the keyboard, then
the host can use simple input-only ports). The
clock and data signals (PS2C and PS2D) are
connected directly to pins on the B connector.
A PS2-style keyboard uses scan codes to
communicate key press data (nearly all
keyboards in use today are PS2 style). Each key
has a single, unique scan code that is sent
whenever the corresponding key is pressed. If
the key is pressed and held, the scan code will
be sent repeatedly once every 100ms or so.
When a key is released, a “F0” key-up code is
sent, followed by the scan code of the released
key. If a key has a “shift” character that is
different than the non-shift character, the same
scan code is sent whether the shift key is
pressed or not, and the host device must
determine which character to use. Some keys,
called extended keys, send an “E0” ahead of
the scan code (and they may send more than
one scan code). When an extended key is
released, an “E0 F0” key-up code is sent,
followed by the scan code. Scan codes for most
keys are shown in the figure below.
A host device can also send data to the
keyboard. Below is a short list of some often-
used commands.
ED Turn on/off Num Lock, Caps Lock, and
Scroll Lock LEDs. The keyboard
acknowledges receipt of an “ED” by
returning an “FA”, after which the host
send another byte to set LED status: Bit 0
sets Scroll Lock; bit 1 sets the Num Lock;
and Bit 2 sets Caps lock. Bits 3 to 7 are
ignored.
EE Echo. Upon receiving an echo command,
the keyboard replies with the same scan
code (“EE”).
F3 Set scan code repeat rate. The keyboard
acknowledges receipt of an “F3” by
returning an “FA”, after which the host
sends a second byte to set the repeat rate.
FE Resend. Upon receiving a resend
command, the keyboard will re-send the
last scan code sent.
FF Reset. Resets the keyboard.
The keyboard should send data to the host only
when both the data and clock lines are high (or
idle). Since the host is the “bus master”, the
keyboard should check to see whether the host
is sending data before driving the bus. To
facilitate this, the clock line can be used as a
“clear to send” signal. If the host pulls the
clock line low, the keyboard must not send any
data until the clock is released (host-to-
ESC
76
` ~
0E
TAB
0D
Caps Lock
58
Shift
12
Ctrl
14
1 !
16
2 @
1E
3 #
26
4 $
25
5 %
2E
Q
15
W
1D
E
24
R
2D
T
2C
A
1C
S
1B
D
23
F
2B
G
34
Z
1Z
X
22
C
21
V
2A
B
32
6 ^
36
7 &
3D
8 *
3E
9 (
46
0 )
45
- _
4E = +
55
BackSpace
66
Y
35
U
3C
I
43
O
44
P
4D
[ {
54 ] }
5B
\ |
5D
H
33
J
3B
K
42
L
4B
; :
4C
' "
52
Enter
5A
N
31
M
3A
, <
41 > .
49 / ?
4A
Shift
59
Alt
11
Space
29
Alt
E0 11
Ctrl
E0 14
F1
05 F2
06 F3
04 F4
0C
F5
03 F6
0B
F7
83 F8
0A
F9
01 F10
09
F11
78
F12
07 E0 75
E0 74
E0 6B
E0 72