3
Windows Driver
Receive Trigger Level
The time when the UART generates an interrupt for received data. It defines
the amount of data necessary to do this. With the 16950 you may select any value from 1
to 128. Other types allow only certain values. Higher values increase performance, lower
values decrease possibility for loss of data. As a reference: the usual value for a 16C550A is
8, leaving space for 8 more bytes to receive.
Transmit Trigger Level
The time when the UART generates an interrupt for sent data. When the
transmit FIFO contains less data than this, the interrupt is issued. This value is not available
with all emulations. Higher values make a smoother transmission of data, but increase the
system load.
Transmit Buffer Length
The amount of data sent to the UART when the transmit FIFO is empty.
This is a complete software item. The value ranges from 1 to the FIFO size of the emulation.
Higher values increase transmission performance. The typical value here is 16, the FIFO size
of a 16550. This value must not be less than the Transmit trigger level. CAUTION: external
hardware - such as a modem - must be able to handle this blocksize, very old systems may
require to reduce this parameter to ‘1’.
Enable TCR
The 16C950 UART used on the H-series cards has some hardware option to get very
high bit rates, up to 3.6 Mbps. Of course these bit rates can not be used on RS 232, but
there are other advantages. The maximum serial speed is raised, so there are more possible
bit rates available in the usual range of RS 232 transmission. This allows to use some more
rather unusual settings for transmission rates, some special hardware may require. Possible
products with RS 422/485 line drivers can use such high bit rates.
Since this option may reduce the transmission accuracy in certain environments, it is disabled
by default.
February 2010
VScom PCIex Card User Manual
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