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Normal Connect Mode (NCM)
Once discovery has been completed, the primary device and MCP2150
(secondary device) can freely exchange data. The MCP2150 can
receive IR data or serial data, but not both simultaneously. The
MCP2150 uses a hardware handshake to stop the local serial port from
sending data while the MCP2150 is receiving IR data. Both the pri-
mary device and the MCP2150 (secondary device) check to make sure
that data packets are received by the other without errors. Even when
data is required to be sent, the primary and secondary devices will still
exchange packets to ensure that the connection has not, unexpected-
ly, been dropped.

When the primary device has finished, it then transmits the close
link command to the MCP2150 (secondary device). The MCP2150
will confirm the close link command, and both the primary device
and the MCP2150 (secondary device) will revert to the NDM state. It
is the responsibility of the host controller program to understand the
meaning of the data received and how the program should respond
to it. It is just as if the data were being received by the host controller
from a UART. Note: The MCP2150 is limited to a data rate of 115.2
kbaud. Data loss will result if this hardware handshake is not
observed. If the NCM mode is unexpectedly terminated for any rea-
son (including the primary device not issuing a close link com-
mand), the MCP2150 will revert to the NDM state 10 seconds after
the last frame has been received. Figure 5.28 shows the connection
sequence.

MCP2150 Operation
The MCP2150 emulates a null modem connection. The application on
the DTE device sees a virtual serial port. This serial port emulation is
provided by the IrDA standard protocols. The link between the DTE
device and the embedded application is made using the MCP2150.
The connection between the MCP2150 and the embedded application
is wired as if there were a null modem connection.
The carrier detect (CD) signal of the MCP2150 is used to indicate that
a valid IrDA standard IR link has been established between the
MCP2150 and the primary device. The CD signal should be moni-
tored closely to make sure that any communication tasks can be com-
pleted. The MCP2150 data signaling rate (DSR) signal indicates that

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