Specifications

Card Setup
Sealevel Systems ULTRA 530.PCI Page 2
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.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 530.PCI in a RS-485 application with existing (i.e. standard RS-232) software drivers.
Header E4 is used to control the RS-485 mode functions for the driver circuit. The selections are:
‘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 E4 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’.