Impulse 7402 - Manual (Page 5)

Card Setup
Sealevel Systems ULTRA COMM+422.PCI Page 2
Card Setup
In all cases J1x is for port 1, J2x - port 2, J3x - port 3 and J4x – port 4.
RS-485 Enable Modes
RS-485 is ideal for multi-drop or network environments. RS-485 requires a
tri-state driver that will allow the electrical presence of the driver to be removed
from the line. The driver is in a tri-state or high impedance condition when this
occurs. Only one driver may be active at a time and the other driver(s) must be
tri-stated. The output modem control signal Request To Send (RTS) is typically
used to control the state of the driver. Some communication software packages
refer to RS-485 as RTS enable or RTS block mode transfer.
One of the unique features of the ULTRA COMM+422.PCI is the ability to be
RS-485 compatible without the need for special software or drivers. This ability
is especially useful in Windows, Windows NT, and OS/2 environments where
the lower level I/O control is abstracted from the application program. This
ability means that the user can effectively use the ULTRA COMM+422.PCI in
an RS-485 application with existing (i.e. standard RS-232) software drivers.
Headers J1B – J4B are used to control the RS-485 mode functions for the driver
circuit. The selections are ‘RTS’ enable (silk-screen ‘RT’) or ‘Auto’ enable
(silk-screen ‘AT’). The ‘Auto’ enable feature automatically enables/disables the
RS-485 interface. The ‘RTS’ mode uses the ‘RTS’ modem control signal to
enable the RS-485 interface and provides backward compatibility with existing
software products.
Position 3 (silk-screen ‘NE’) of J1B – J4B is used to control the RS-485
enable/disable functions for the receiver circuit and determine the state of the
RS-422/485 driver. The RS-485 ‘Echo’ is the result of connecting the receiver
inputs to the transmitter outputs. Every time a character is transmitted; it is also
received. This can be beneficial if the software can handle echoing (i.e. using
received characters to throttle the transmitter) or it can confuse the system if the
software does not. To select the ‘No Echo’ mode select silk-screen position
‘NE’.
For RS-422/530/449 compatibility remove the jumpers at J1B – J4B.
Examples on the following pages describe all of the valid settings for J1B – J4B.