Digilent 410-044-10P-KIT User Manual
Page 29
Spartan-3 Starter Kit Board User Guide
29
UG130 (v1.1) May 13, 2005
1-800-255-7778
Keyboard
R
The host can also send data to the keyboard.
Table 6-3
provides a short list of some often-
used commands.
The keyboard sends data to the host only when both the data and clock lines are High, the
Idle state.
Because the host is the “bus master”, the keyboard checks whether the host is sending data
before driving the bus. 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.
The keyboard sends data to the host in 11-bit words that contain a ‘0’ start bit, followed by
eight bits of scan code (LSB first), followed by an odd parity bit and terminated with a ‘1’
stop bit. When the keyboard sends data, it generates 11 clock transitions at around 20 to
30 kHz, and data is valid on the falling edge of the clock as shown in
Figure 6-3:
PS/2 Keyboard Scan Codes
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
Back Space
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
UG130_c6_03_042404
Table 6-3:
Common PS/2 Keyboard Commands
Command
Description
ED
Turn on/off Num Lock, Caps Lock, and Scroll Lock LEDs. The keyboard acknowledges receipt of
an “ED” command by replying with an “FA”, after which the host sends another byte to set LED
status. The bit positions for the keyboard LEDs appear in
Table 6-4
. Write a ‘1’ to the specific bit to
illuminate the associated keyboard LED.
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 resends the last scan code sent.
FF
Reset. Resets the keyboard.
Table 6-4:
Keyboard LED Control
7
6
5
4
3
2
1
0
Ignored
Caps
Lock
Num
Lock
Scroll
Lock