Matrix Orbital LCD/VFD Legacy - Manual (Page 22)

change and the module will return to the originally set serial number.
5.1.12 Read Serial Number (254 53)
This command will return, over the RS-232 interface, the two-byte serial number of the module as it was
previously stored.
5.1.13 Read Version Number (254 54)
This command will return the firmware version number of the display. This command returns a 1-byte
hex value.
5.2 Flow Control
The display has built in flow control which may be useful when long strings of text are downloaded to
the display. Flow control is enabled or disabled by two commands. If flow control is enabled, the display
will return an "almost full" message (0xFE) to the controller when its internal buffer fills to a defined level,
and an "almost empty" message (0xFF) when the buffer contents drop to a defined level.
5.2.1 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 controller. When the buffer empties so that only [empty]
bytes remain the display will return an "almost empty" message (0xFF) to the 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 buffer is
almost full even though it may have already thrown rejected data away. The buffer size for the display is 80
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 [full] 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 of should be set to 16 or greater.
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