Card Setup - SeaLevel ULTRA 485+2.PCI User Manual

Card Setup

In all cases J1x refers to settings for the first port and J2x refers to settings for the second port.
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 485+2.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 485+2.PCI in a RS-485 application with existing (i.e.
standard RS-232) software drivers.
Headers J1B and J2B 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 and J2B 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 compatibility remove the jumpers at J1B and J2B.
Examples on the following pages describe all of the valid settings for J1B and J2B.
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© Sealevel Systems, Inc. 7204 Manual | SL9061 7/2021