Measurement Computing PCI-COM422/485 - Manual (Page 10)

6
Figure 2-4. TTY Settings
4. Launch the ComApp again. You will get a second ComApp window. Go to the Settings
menu and configure the second port. Note that you must use the same settings on both
ports for this test to work properly.
5. On both open ComApp windows, go to the Action menu and select Connect.
6. After connection, move the cursor to either ComApp window. Whatever is typed in that
window should be immediately displayed in the other. You can also test port
operations by selecting the Transfer menu and clicking on Send Data Block. A large
block of ASCII characters will automatically be sent, and should appear on the other
ComApp window. The transfer block can be used to send ASCII characters or hex numbers in
user defined block sizes.
2.5 RS-485 AUTO-ENABL ED MODE
The PCI-COM422/485 board incorporates a software selectable “Auto-Enable” mode. This mode can be
used for applications that require reduced software overhead or to remove the burden of flow control
from the application itself. The Auto-Enable mode can be used for the transmission of single characters or
for block transfers of multiple characters in RS485 mode.
When using Auto-Enable mode, the PCI-COM485’s on-board state machine enables the transmitter’s
output driver once the falling edge of a start bit is detected. The length of time the output driver is enabled
is dependent on the combination of start, data, parity and stop bits the user selects.
Note: The user can select from any combination of start, data and parity bits, although this mode does
limit the transmission to a single stop bit (1.5 and 2 stop bits are not allowed in this mode and if used will
result in data integrity errors).
2.6 EXTENDED BAUD R ATE OPERATION
Though it isn’t possible to set baud rates greater than 115.2 kbaud on the PCI-COM series using the standard
Windows Communications Port Properties dialog, the board and operating system are actually capable of operating
at transfer rates up to 460.8 kbps. The PCI-COM series boards have a programmable divider between the on-board
system clock and the UART. This divider can be set using the Advanced tab that was added to the Windows 95/98
Communications Port Properties dialog or the PCIcom applet added to the NT Control Panel during the PCI-COM
software installation.