Matrix Orbital GLC24064 - Manual (Page 25)

4.3.1 Enter Flow Control Mode (254 58 [full][empty])
NOTE Flow control applies only to the RS-232 interface. It is not available for I 2 C.
This command enables flow control. When the buffer fills so that only [full] bytes are available, the display
will return an "almost full" message (0xFE) to the micro-controller. When the buffer empties so that only
[empty] bytes remain the display will return an "almost empty" message (0xFF) to the micro-controller.
The display will return the "almost full" message for every byte sent to the display until the used buffer
space once more drops below the [full] level.
Whether the user is in ’Flow control mode’ or not, the module will ignore display or command bytes
which would over-run the buffer. While in ’Flow control mode’ the unit will return 0xFE when the buffer is
almost full, even though it may have already thrown rejected data away. The buffer size for the display is 96
bytes.
When using this command in an application, selection of the value for the buffer almost full should be
considered very carefully. This is a critical aspect of using this command to it’s full potential. When using a
host system or PC which contains a FIFO, the user should set the value of equal to or greater than the size of
the FIFO. The reason for this is that the FIFO may be full when the host system receives 0xFE. In the case
of 16550 UART the size at its maximum is 16, therefore the value should be set to 16 or greater.
WARNING This mode must not be used during loading of fonts and
bitmaps. It is highly recommended for use with direct screen write and
multiple pixel placements.
4.3.2 Exit Flow Control Mode (254 59)
This command turns off flow control. Bytes may overflow the buffer without warning.
5 Fonts and Graphics Files
5.1 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.
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