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© Sealevel Systems, Inc. 7402 Manual | SL9063 7/2021
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 th
e 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
–
J4B.
Examples on the following pages describe all of the valid settings for J1B
–
J4B.
