Matrix Orbital GLK12232-25-SM Legacy - Manual (Page 24)

6.5.5 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.
6.5.6 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
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.
6.5.7 Set debounce time (254 85 [time])
[time] is in increments of 6554 microseconds.
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.
7 Fonts and Graphics Files
7.1 General
Matrix Orbital graphic modules contain a sophisticated file system for storing and retrieving font infor-
mation, bitmaps and system parameters; not unlike the way that a computer deals with files on a hard drive.
However, the modules use no moving parts, therefore, data is stored far more reliably than data on a home
PC.
Operationally, there is one important difference between the Matrix Orbital file system and that of a PC.
While a PC will allow fragmentation of its files across the available file space, the Matrix Orbital file system
takes great care to ensure that all parts of a file are stored together. This system works well to maximize
storage space and operational efficiency. However, during file downloads the modules may need to spend
considerable time moving files to make room for the new file. This delay during download can be as much
as a minute, but generally it will not exceed 10 seconds.
When a file is being downloaded with the same ’name’ or reference number as a previously existing
file, the old file needs to be deleted first. We cannot know if the new file is exactly the same size as the old
file since the space vacated by the old files is filled by moving previously existing files down to fill up the
vacated space. This ensures that no file space is wasted.
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