Card Setup; Rs-485 Enable Modes - SeaLevel ULTRA 530.LPCI User Manual

Card Setup

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 530.LPCI 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 530.LPCI in a RS-485 application with existing (i.e.
standard RS-232) software drivers.
Header E5 is used to control the RS-485 mode functions for the driver circuit. The
selections are:
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'.
© Sealevel Systems, Inc.
'Auto' enable (silk-screen 'AT'). The 'Auto' enable feature automatically
enables/disables the RS-485 interface via on board circuitry.
'RTS' enable (silk-screen 'RT') The 'RTS' mode uses the 'RTS' modem control
signal to enable the RS-485 interface and provides backward compatibility with
existing software products.
'DTR' enable (silk-screen 'DT') The 'DTR' mode uses the 'DTR' modem
control signal to enable the RS-485 interface, provides backward compatibility
with existing software products and with the Oxford Semiconductor 16C950
RS-485 enable feature
'Output One' enable (silk-screen 'OP') This mode uses the 'OP1' control signal
to enable the RS-485 interface and provides backward compatibility with
existing software products and with the Exar 16C850 RS-485 enable feature
'No Echo' (silk-screen 'NE') of E5 is used to control the RS-485 enable/disable
functions for the receiver circuit and determine the state of the RS-422/485
driver.
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ULTRA 530.LPCI User Manual