5
© Sealevel Systems, Inc.
7105-DB9 Manual | SL9053 9/2021
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 485.OPTO22
is the ability to be RS-485 compatible without the
need for special software or drivers. This ability is especially useful in 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.OPTO22
in an RS-485 application with existing (i.e., standard RS-232) software drivers.
Switch SW2 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 signa
l to enable the RS-485
interface and provides backward compatibility with existing software products.
‘No Echo’
(silk-
screen ‘NE’) is used to control the RS
-485 enable/disable functions for the receiver based
on the state of the RS-422/485 transmitter. 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’.
Clock Modes
The
ULTRA 485.OPTO22
employs a unique clocking option that allows the end user to select from divide
by 4 and divide by 1 clocking modes. SW2 positions 1 and 2 select the Divide by 1 (silk-screen D1) and
divide by 4 (silk-screen D4) modes.
To select the Baud rates commonly associated with COM: ports (i.e.,
2400, 4800, 9600, 19.2, … 115.2K
Bps), set switch SW2 in the divide by 4 mode (silk-screen D4).
To select data rates up to the maximum of 460.8K bps, set switch SW2 in the divide by 1 (silk-screen D1)
position. Please refer to the following page for these additional data rates.
Do not set both switches on or invalid clocking will occur.
