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Technical Description
OMG-COMM2-EX Page 7
Technical Description
The OMG-COMM2-EX adapter utilizes the 16550 UART chip. This chip features
programmable baud rate, data format, interrupt control and has a 16 byte transmit
and receive FIFO.
Features
• Full independent operation of ports allowing two ports RS-232, two ports
RS-422/485 or one port of each.
• Addressable as COM1: - COM4: or any other I/O address up to 3FF Hex.
• ‘Shareable’ IRQs allow more than one port to share a single IRQ provided
the proper driver is used..
• IRQs 2/9-5, 7, 10, 11, 12, 15 supported
• Support for non-standard baud rates available. These baud rates (such as
31.25K or 76.8K baud) are supported by installing a different oscillator.
Please consult Technical Support for more information.
Modem Control Signal Considerations
Some software packages require the use of the modem handshake signals such
as CTS or DCD. Refer to your application software manual to determine the
requirements for modem control signals. If no requirements are mentioned, a safe
configuration is to tie DTR to DSR and DCD, and tie RTS to CTS. This
configuration will typically satisfy the modem control signal requirements for
most communications software.
Line Termination
Typically, each end of the RS-422/485 bus must have line terminating resistors. A
100 ohm resistor is across each RS-422/485 input and a 1K ohm pull-up/pull-
down combination bias the receiver inputs. If more than two RS-485 nodes are
configured in a multi-drop network, only the nodes at each end of the bus should
have the 100 ohm resistors installed.