connector. 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.
9.1.1
I
2
C Interface
The keypad is read by I
2
C 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
I
2
C function can be found in the I
2
C specification by Phillips.
9.1.2
RS232 Interface
By default on any press of a key, the module will immediately send out the key code at the selected baud
rate. This behavior can be modified using commands found in the next section.
9.2
Auto Transmit Key Presses On
Syntax
Hexadecimal
0xFE 0x41
Decimal
254 65
ASCII
254 “A”
Description
In this mode, all key presses are sent immediately to the host system
without the use of the poll keypad command. This is the default mode
on power up.
NOTE
This command is not available in I
2
C.
Remembered
Yes
Default
On
9.3
Auto Transmit Key Presses Off
Syntax
Hexadecimal
0xFE 0x4F
Decimal
254 79
ASCII
254 “O”
Matrix Orbital
LK202-25
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