Matrix Orbital VK204-25 Legacy - Manual (Page 40)

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”
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