Instruction Manual

Technical Description
Sealevel Systems COMM+2/EX Page 8
Technical Description
The COMM+2/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
• Fully 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 Sealevel Systems Technical Support for more
information.
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.
Connector Pin Assignments
RS-232 (Male DB9)
Name Pin # Mode
TD Transmit Data 3 Output
RTS Request To Send 7 Output
DTR Data Term Ready 4 Output
GND Ground 5
RD Receive Data 2 Input
DCD Data Carrier Detect 1 Input
DSR Data Set Ready 6 Input
CTS Clear To Send 8 Input
RI Ring Indicator 9 Input
Note: These assignments meet EIA/TIA/ANSI-574 DTE for DB-9 type connectors.
RS-422/485 (Male DB9)
Signal Name Pin # Mode
GND Ground 5
TX + Transmit Data Positive 4 Output
TX- Transmit Data Negative 3 Output
RTS+ Request To Send Positive 6 Output
RTS- Request To Send Negative 7 Output
RX+ Receive Data Positive 1 Input
RX- Receive Data Negative 2 Input
CTS+ Clear To Send Positive 9 Input
CTS- Clear To Send Negative 8 Input