Matrix Orbital LK202-25 Legacy - Manual (Page 26)

4.5.4 Auto transmit keypresses off (254 79) (R)
In this mode, up to 10 keypresses are buffered until the unit is polled by the host system via the poll
keypad command. Issuing this command places the unit in polled mode.
4.5.5 Clear key buffer (254 69)
This command clears any unread keypresses. In a menuing application, if the user presses a key which
changes the menu context, any following key presses may be inaccurate and can be cleared out of the buffer
between menu changes to prevent jumping around the menu tree. It may also be used to, in effect, reset the
keypad in case the host application resets for whatever reason.
4.5.6 Poll keypad (254 38)
This command returns any unbuffered keypresses via the RS-232 interface. The host system must be
set up to receive the key codes. When the display receives this command it will immediately return any
unbuffered keypresses which may have not been read already. If there is more than one keypress buffered,
then the high order bit (MSB) of this returned keycode will be set (1). If this is the only buffered keypress,
then the MSB will be reset (0). If there are no buffered keypresses, then the returned code will be 0x00.
Please note that to make use of this command, the "Auto transmit keypress" mode should be off.
4.5.7 Set debounce time (254 85 [time]) (R)
[time] is in increments of 6.554 milliseconds.
This command sets the time between key press and key read. 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 52 ms, which is adequate for most membrane keypads.
5 Bar Graphs and Special Characters
The display includes the ability to draw bar graphs (either horizontal or vertical) and allows users to
define up to eight special characters
Eight characters (ASCII values 0x00 to 0x07) are set aside for use with bar graphs, user defined char-
acters, and large numbers. Since the same 8 characters are used for each function, the functions may not
be used simultaneously. The characters may be defined or redefined at any time by issuing the commands
shown in this section. Once defined, they may be used either by means of the bar graph commands, or by
simply issuing one of the ASCII values 0x00 to 0x07, which are not prefixed by the command byte, 254.
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