Impulse 7201 - Manual (Page 5)

Card Setup
Sealevel Systems ULTRA COMM+2.PCI Page 2
Card Setup
In all cases J1x refers to settings for the first port and J2x refer 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 COMM+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 COMM+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.
The following examples describe all of the valid settings for J1B and J2B.
Interface Mode Examples J1B – J2B
AT RT NE
Figure 1- Headers J1B and J2B, RS-422
AT RT NE
Figure 2 - Headers J1B and J2B, RS-485 ‘Auto’ Enabled, with ‘No Echo’