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PDF LK204-25 Data sheet ( Hoja de datos )
| Número de pieza | LK204-25 | |
| Descripción | User Manual | |
| Fabricantes | Matrix | |
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LK204-25
User Manual
Important: Read page 2 before applying power.
1 page  
The Keypad Interface
Keypad Interface via I²C
The keypad is read by I²C master read. In short, this means that a read of the module will always return the first unread key
press. A read is initiated by writing to the module with its base address plus 1, then clocking the module’s return byte after
the module releases the SDA line. Much more detail on this basic I²C function can be found in the I²C specification by
Philips.
The module contains a ten key press buffer so that it can be polled for key presses at an infrequent rate (every 500 to 1000
mS is typical). All returned key presses indicate the presence or absence of additional logged key presses by the most
significant bit (MSB - bit 7). If the user has pressed two keys since the last poll of the keypad interface, the first read will
return the key code with bit 7 set and the second read will return the key code with bit 7 clear. The application must take
www.DataSheeint4tUo.acocmcount this bit to keep up with user key presses. If there are no keypresses detected, the module will return zero
(0x00).
Keypad Interface via RS - 232
By default on any press of a key, the module will immediately send out the key code at the selected baud rate.
Auto Transmit:
If the auto transmit mode is on (default) then on any keypress, the module will immediately send out the key code at the
selected baud rate. If auto transmit is off, when the poll command is sent, the module will immediately send the key code.
Keypad Interface (Both I²C and RS - 232)
Auto Repeat:
Two Modes of auto repeat are available and are set via the same command.
1)Resend Key Code: This mode is similar to the action of a keyboard on a PC and is set via the '~" command with a value
of 0 as outlined in the Command Set section of this manual. In this mode, when a key is held down, the key code is trans-
mitted immediately followed by a 1/2 second delay. After this delay, key codes will be sent via the RS - 232 interface at a
rate of about 5 codes per second. This mode has no effect if polling or if using the I²C interface.
2)Key down / Key up codes: This mode may be used when the typematic parameters of the Resend Key code mode are
unacceptable or if the unit being operated in polled mode. The host system detects the press of a key and simulates an auto
repeat inside the host system until the key release is detected. This mode is entered via the '~' command with a data value
of (0x01). In this mode, when a key is held down, the key code is transmitted immediately and no other codes will be sent
until the key is released. On the release of the key, the key release code transmitted will be a value equal to the key down
code plus 40 hex. The key code associated with key code '0' (0x30) is pressed, the release code is 'p' (0x70). In RS - 232
polled mode or via the I²C interface, theses codes are available in the same manner as keypresses without auto repeat;
however, the user should be careful to ensure that the poll rate is high enough so that simulated key repeats are avoided
after the release of the key but before the next poll.
Physical Layout:
The returned key codes are as follows, but note that your keypad may be laid out in a different pattern. If this is the case, the
user will need to interpret the key codes differently. The diagram 1 shows the logical layout (row 1, column 1 in upper left).
The connector for the keypad is a 10 pin .1" spacing male header. Pin 1 is indicated on the connector layout diagram. Pins 1
through 5 are columns and pins 6 through 10 are row. The keypad is scanned whenever a key is pressed. There is no
continuous key scan. This means that key presses are dealt with immediately without any appreciable latency. This also
prevents electrical noise which is often caused by continuous key scans.
5
5 Page 
Set Debounce Time
ASCII 'U', Hex 55, Decimal 85
Syntax 0xFE 0x55<number to define debounce time>
To set the time between key press and key read, send a command prefix followed by the character 'U' and a number to
define the debounce time. All key types with the exception of latched piezo switches will"bounce" for a varying time,
depending on their physical characteristics. The default debounce time for the module is about 65mS, which is adequate
for most membrane keypads. This time equates to a setting of 8 using this command as there is a debounce time resolution
of 8192 microseconds.
Create Custom Character
ASCII 'N', Hex 4E, Decimal 78
Syntax 0xFE 0x4E<character between 0x00 and 0x07><8 bytes>
w w w . D a t a S hTeheist 4cUom. cmo mand creates a custom character. For the LK204-25 the user can have up to eight custom characters. To execute
this command, send a command prefix followed by the character 'N'. The display will now await the number which identi-
fies the custom character. This number must be between 0x00 and 0x07. When the module determines what character it's
working on, then the user must send 8 bytes which define the display character. See the diagram below for and explanation
of the display character structure.
Diagram A
MSB
LSB
*** 1 2 3 4 5
* * * 6 7 8 9 10
* * * 11 12 13 14 15
* * * 16 17 18 19 20
* * * 21 22 23 24 25
* * * 26 27 28 29 30
* * * 31 32 33 34 35
* * * 36 37 38 39 40
Data Byte 1
Data Byte 2
Data Byte 3
Data Byte 4
Data Byte 5
Data Byte 6
Data Byte 7
Data Byte 8
Pixel Layout of Display Characters
12345
6 7 8 9 10
11 12 13 14 15
16 17 18 19 20
21 22 23 24 25
26 27 28 29 30
31 32 33 34 35
36 37 38 39 40
Cursor Line
General Purpose Output On
ASCII ' V', Hex 56, Decimal 86
Syntax 0xFE 0x56<hex number corresponding to output>
To turn a general output purpose on, send a command prefix followed by the character 'V' and hex number which corre-
sponds to the output which will be turned on. To turn on output five, the sequence would be:
<command prefix>
<command>
<hex number corresponding to output>
0xFE
0x56
05H
11
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