VK202-25 rev. 05
25
6.1.13 Read Version Number 254 54)
This command will return the firmware version number of the VK202-25 as a 1 byte hex value over RS232
only.
6.2 Flow Control
The VK202-25 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 (see Table 7-4 and the next two
sections). If flow control is enabled, the VK202-25 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.
6.2.1 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 VK202-
25 will return an "almost full" message (0xFE) to the controller. When the buffer empties so that only
[empty] bytes remain the VK202-25 will return an "almost empty" message (0xFF) to the controller.
The VK202-25 will return the "almost full" message for every byte sent to the VK202-25 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 overrun 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 VK202-25 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.
6.2.2 Exit Flow Control Mode (254 59)
This command turns off flow control. Bytes may overflow the buffer without warning.
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