UR5HC703-600 SerialCoder data sheet
SerialCoder 600 UR5HC703-600
Extremely Low-Power Keyboard
Encoder Interfaces RS-232
Semtech, SerialCoder, and KeyCoder are
registered trademarks of Semtech Corporation.
All other trademarks belong to their respective
companies.
Copyright 1999-2002 Semtech Corporation
DOC5-703-600-DS-106
www.semtech.com
1
HID & SYSTEM MANAGEMENT PRODUCTS, KEYCODER FAMILY
DESCRIPTION
FEATURES
1
8
9
32
25
24
16
17
COL03
COL04
COL05
COL06
VDD2
RESET
VSS2
VDD
ROW6
ROW5
ROW4
ROW3
ROW2
ROW1
ROW0
COL15
OCSIN
OSCOUT
VSS
COL07
COL08
COL09
COL10
COL11
COL02
COL01
COL00
COL14
COL13
TxD
COL12
ROW7
UR5HC703-600-FG
LQFP
8 x 16 matrix encoding
9600 Baud 8N1 serial data format
IC is independent of the
keyboard layout
Extremely low-power operation,
transparent to the host
Average current consumption of
less than 1 A at room
temperature; 10 A at 85C
TTL/CMOS output-only
asynchronous serial interface
to the host (direct connection to
the UART)
Very simple serial protocol -- two-
byte identification string on power-
up; single-byte matrix-position for
each key-press or key-release
Robust algorithm for ghost-key
elimination
The SerialCoder 600
UR5HC703-600 is an extremely low-
power, "off-the-shelf" serial keyboard
encoder. Robust, tiny and flexible,
the IC is a good match for any
application where complicated
keyboard protocols are not required
and asynchronous serial interface
hardware is available.
The SerialCoder 600 provides
unprecedented power consumption
minimization, making it ideal for use
in add-on keyboards for handheld
and cellular / web phones and
single-board systems designed for
portable applications. The IC
provides extremely low-power
operation, transparent to the host.
Power consumption is reduced to
just the circuit's leakage when all
keys are released. The average
current consumption is less than 1
A at room temperature and 10 A
at 85C.
If a single key or groups of keys are
stuck in the depressed position, the
IC will enter a total shutdown after a
10-minute wait -- to protect against
unintended and unnecessary
discharge of the batteries in the
host.
The SerialCoder 600 is simple to
implement. It requires few external
components and utilizes a tiny, low-
profile 32-pin LQFP package that
measures 7mm x 7mm.
Semtech also offers other products
in the SerialCoder series.
APPLICATIONS
Add-on accessory keyboards for
personal digital assistants (PDAs)
and hand-held PCs (H/PCs)
Built-in keyboards for PDAs and
H/PCs
Portable personal computers
Instrumentation
Remote control
Cellular phones
PIN ASSIGNMENTS
PRELIMINARY
SERIALCODER 600 FUNCTIONAL DIAGRAM
ORDERING CODE
Copyright 1999-2002 Semtech Corporation
DOC5-703-600-DS-106
www.semtech.com
2
TxD
4
Data
Buffer
Key
Matrix
Interface
Communication
Interface
Matrix
Scan Logic
Reset Logic
Oscillator
Power Supply
_RESET
OSCIN
_OSCOUT
8
16
ROW0-ROW7
COL00-COL15
Package Options
Pitch
T
A
= -20C to +85
32-pin plastic LQFP
0.8 mm
UR5HC703-600-FG
Other Materials
Type
Order number
SerialCoder 600 eval. kit
Evaluation kit
EVK5-703-600
PIN DEFINITIONS
Copyright 1999-2002 Semtech Corporation
DOC5-703-600-DS-106
www.semtech.com
3
Mnemonic
Pin #
Type
Name and Function
Power Supply
V
DD
, V
DD
2
8, 5
PWR
Positive supply voltage
Vss, Vss2
11, 7
PWR
Negative power supply:
Signal ground
Reset
_RESET
6
I
Hardware reset pin: Reset input
for orderly start-up. Low logic level is
required until power supply reaches
minimum operating voltage.
Oscillator pins
OSCIN
9
I
Oscillator input: Connect ceramic
resonator with built-in load capacitors;
2 MHz operating frequency
_OSCOUT
10
O
Oscillator output: Connect ceramic
resonator with built-in load capacitors
Host interface
TxD
27
O
Serial data output: Idle at high
voltage (logical 1), non-inverted data
(direct connection to the UART)
Scanned
matrix pins
ROW0-ROW7
18-25
I, pup
Row matrix inputs: With pulsed
pull-up current sources
COL00-COL15
30-32,
O
Column matrix output
1-4,
12-16,
26,
28-29, 17
Copyright 1999-2002 Semtech Corporation
DOC5-703-600-DS-106
www.semtech.com
4
"GHOST" KEYS
KEYBOARD SCANNER
In any scanned contact switch
matrix, whenever three keys
defining a rectangle on the switch
matrix are pressed at the same
time, a fourth key positioned on the
fourth corner of the rectangle is
sensed as being pressed. This is
known as the "ghost" or "phantom"
key problem.
Figure 1: "Ghost" or "Phantom" Key
Problem
Although the problem cannot be
totally eliminated without using
external hardware, there are
methods to neutralize its negative
effects for most practical
applications. Keys that are
intended to be used in
combinations should be placed in
the same row or column of the
matrix, whenever possible. Shift
keys (Shift, Alt, Ctrl, Window)
should not reside in the same row
(or column) as any other keys. The
SerialCoder 600 has built-in
mechanisms to detect the
presence of "ghost" keys.
Actual key presses
"Ghost"
Key
The encoder scans a keyboard organized as an 8 row by 16 column matrix
for a maximum of 128 keys. Smaller size matrixes can also be
accommodated simply by leaving unused pins open. The
SerialCoder 600 provides internal pull-ups for the row input pins. When
active, the encoder selects one of the column lines (C0-C15) every 512 S
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 serial communication channel.
N-key rollover means the code(s) corresponding to each key press are
transmitted to the host system as soon as that key is debounced, indepen-
dent of the release of other keys.
When a key is released, the corresponding break code is transmitted to the
host system. Several keys can be held pressed at the same time.
However, if two or more key closures occur within a time interval of less
than 5 ms, an error flag is set, and those closures are not processed. This
feature protects against the effects of accidental key presses.
N-KEY ROLLOVER
PROTOCOL
Copyright 1999-2002 Semtech Corporation
DOC5-703-600-DS-106
www.semtech.com
5
Serial transmissions are at the rate of 9600 Baud, 8 data bits, no parity,
least significant bit is transmitted first, idle/stop level is high (logical 1), start
bit level is low (logical 0), non-inverted data.
Within 5ms after the power-up the IC sends a two-byte identification string
of 0xF9, 0xFB. These two bytes are transmitted only once after each reset
of the IC.
These two ID values also represent key release action in the locations
[Row=1, Column=15] and [Row=3, Column=15] on the key matrix. Since
the values of these bytes represent release action of the keys, extraneous
characters will never be generated, even if synchronization between the
driver and IC is lost, or power fluctuations/erroneous resets are applied to
the chip.
If logistics of the driver do not permit "shared" use of the identification
values 0xF9 and 0xFB, then the user is advised not to incorporate keys in
the locations [Row=1, Column=15] and
[Row=3, Column=15] for the key matrix design.
Subsequent single-byte transmissions indicate the row (0-7), column
(0-15), and press/release action for each change of the state of every key.
If after the current key release all of the keys on the key matrix are in the
released state, the last transmission is repeated. Host's driver looking for
two bytes with exactly the same value and key release indication (b7=1)
can recognize that the keyboard is completely idle.
Byte Transmission
Bit Number
Comment
b7
0 for key press, 1 for key release
b6
Column location in the key matrix (0-15)
b5
b4
b3
b2
Row location in the key matrix (0-7)
b1
b0
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