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© Sealevel Systems, Inc. 7802ec &7802ecS Manual | SL9680 11/2022
Card Setup
Address and IRQ Selection
The 7802ec is automatically assigned memory addresses and IRQs by your motherboard BIOS or by a “Plug-
n-Play” Operating System. Adding or removing other hardware or moving the adapter to another slot may
change the assignment of memory addresses and IRQs.
Clock Modes and Baud Rates
The 7802ec derives a 125MHz clock from the PCI express link for the Baud Rate Generator (BRG) which is
divided by a clock prescaler (1 or 4) and a 16-bit clock divisor to obtain a sampling clock of 16X, 8X, or 4X
the serial data rate. The BRG offers a wide range of possible baud rates. Under Windows and Linux, the
best choice of divisor is made automatically by the driver. The bit rate error is within the +/– 2%
recommended tolerance for proper serial communication.
Electrical Interface Selection via Hardware
Each serial port on the 7802ec has the ability to be used as RS-422 or RS-485. Configuration is selectable
via independent per-port DIP switches. Please use the following examples to configure your adapter.
Mode selection via hardware (DIP switches)
M1 Switch
M0 Switch
Mode
OFF
OFF
Reserved (Tri-state)
OFF
ON
RS-422 (Default)
ON
OFF
RS-485 with Echo
ON
ON
RS-485 without Echo
RS-485 Enable Modes
RS-485 is ideal for multi-drop or network environments. RS-485 requires a tristate driver that will allow the
electrical presence of the driver to be removed from the line. The driver is in a tristate 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. Under Windows, configuring a 7802ec port to RS-485 sets the port to automatically assert its output
when transmitting. In RS-485 mode under Windows the port is also set to automatically de-assert its output
at the end of each transmission, returning the driver to tristate so that other drivers can transmit on the line.