UR5HC418 Datasheet, PDF (3/14 Pages) Semtech Corporation – AT / PS/2 - Compatible Keyboard Encoder

FUNCTIONAL DESCRIPTION
The DeskCoder^TM consists
functionally of seven major sections
shown in the functional diagram on
the previous page: the keyboard
encoder, a 16-bit timer, the mode
control unit, the data buffer, the
interrupt control, the PC commun-
ication channel and the 8042
emulation channel. All sections
communicate with each other and
operate concurrently.
KEYBOARD ENCODER
The controller continuously scans a
keyboard organized as an 8 row by
16 column matrix for a maximum of
128 keys. Smaller-size keyboards
are supported provided that all
unused row lines are pulled to Vcc.
The controller selects one of the 16
column lines (C0-C15) every 512
microseconds and then reads the
row data lines (R0-R7). A key
closure is detected as a zero in the
corresponding position of the
matrix.
A complete scan cycle for the entire
keyboard takes approximately 9.2
mS. Each key found pressed is
debounced for a period of 20 mS.
Once the key is verified, the
corresponding key code(s) are
loaded into the transmit buffer of the
PC communication channel.
Status LED indicators
The controller provides an interface
for three LED shift status indicators.
All three pins are active low to
indicate the status of the host
system (Num Lock, Caps Lock and
Scroll Lock) and are set by the
system.
PIN DEFINITIONS
Mnemonic
VCC
VSS (GND)
OSCI
OSCO
_RESET
EKC1
DIP PLCC
40 44
20 22
39 43
38 42
1
1
37 41
QFP
38
17
37
36
41
35
VX
VXA
RP
KC
KD
EKD
EKC
_IRQ
R0-R5
R6
R7
R7A
C0-C4
C5-C7
C8-C15
C4A
CL
NL
SL
NC
3
4
43
3
6
7
2
8
9
4
7
8
3
10 11
6
9 10
5
2
2
42
29-34
5
36
12-16
17-19
28-21
32-37
6
39
40
13-17
19-21
31-24
18
11 12
4
5
35 38
23
27-32
1
34
8-12
13-15
26-23
21-18
7
44
33
39-40
16, 22
Type Name and Function
I Power Supply: +5V
I Ground
I Oscillator input
O Oscillator output
I Reset: apply 0V to provide orderly start-up
I External Keyboard Clock 1:connects
to external keyboard clock line and is used
to generate an interrupt for every clock line
transmission
I Tie to VCC
I Tie to VCC
I Tie to VCC
I/O Keyboard Clock: connects to
PC keyboard port clock data line
I/O Keyboard Data: connects to PC port
data line
I/O External Keyboard Data: connect to
external keyboard data line
I/O External Keyboard Clock: connects
to external keyboard clock line
I/O Interrupt Line: reserved for low power
applications
I Row Data Inputs
I
I
I
O Column Select Outputs: select one of
O 16 columns
O
O
O
O Caps Lock LED
O Num Lock LED
O Scroll Lock LED
No Connects: these pins are unused
Note: An underscore before a pin mnemonic denotes an active low signal.
KEYBOARD ENCODER, (CON’T)
Scan Code Table Sets
The UR5HC418 supports all three scan code table sets. Scan code table
set 3 allows the user to program individual key attributes such as
make/break and Typematic or single-touch action. For more information,
refer to the IBM Technical Reference Manuals. Custom scan code tables,
including macros, are also available.
Switch Matrix Encoding
Each matrix location is programmed to represent either a single key or a
key combination of the IBM 101/102/104 standard keyboard.
Copyright ©1997-2001 Semtech Corporation
3
DOC5-418-DS-109
www.semtech.com