MCP2140 Microchip Technology, Inc., MCP2140 Datasheet - Page 51

• Manufacturer Part Number: MCP2140
• Description: The MCP2140 Embeds Irda Protocol Handling And Bit Encoding/decoding, And Provides The Lowest Cost, Lowest Power Consumption Solution For Adding Irda Connectivity to Embedded Systems
• Manufacturer: Microchip Technology, Inc.

C.2
Discovery mode allows the Primary device to deter-
mine the capabilities of the MCP2140 (Secondary
device). Discovery mode is entered once the MCP2140
(Secondary device) has sent an XID response to the
Primary device and the Primary device has completed
sending the XIDs and then sends a Broadcast ID. If this
sequence is not completed, then a Primary and
Secondary device can stay in NDM indefinitely.
When the Primary device has something to do, it
initiates Discovery. Discovery has two parts. They are:
• Link initialization
• Resource determination
The first step is for the Primary and Secondary devices
to determine, and then adjust to, each other’s hardware
capabilities. These capabilities are parameters like:
• Data rate
• Turn around time
• Number of packets without a response
• How long to wait before disconnecting
Both the Primary and Secondary device begin commu-
nications at 9600 baud, which is the default baud rate.
The Primary device sends its parameters, then the
Secondary device responds with its parameters. For
example, if the Primary supports all data rates up to
115.2 kbaud and the Secondary device only supports
9.6 kbaud, the link will be established at 9.6 kbaud.
Once the hardware parameters are established, the
Primary device must determine if the Secondary device
has the resources it requires. If the Primary device has
a job to print, then it must know if it’s talking to a printer,
not a modem or other device. This determination is
made using the Information Access Service (IAS). The
job of the Secondary device is to respond to IAS que-
ries made by the Primary device. The Primary device
must ask a series of questions like:
• What is the name of your service?
• What is the address of this service?
• What are the capabilities of this device?
When all the Primary device’s questions are answered,
the Primary device can access the service provided by
the Secondary device.
2003 Microchip Technology Inc.
Note:
Discovery Mode
The MCP2140 is limited to a data rate of
9.6 kbaud.
Preliminary
C.3
Once discovery has been completed, the Primary
device and Secondary device can freely exchange
data.
Both the Primary device and the 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 hasn’t,
unexpectedly, been dropped. When the Primary device
has finished, it then transmits the close link command
to the Secondary device. The Secondary device will
confirm the close link command and both the Primary
device and the Secondary device will revert to the NDM
state.
Note:
Normal Connect Mode (NCM)
If the NCM mode is unexpectedly termi-
nated for any reason (including the Primary
device not issuing a close link command),
the Secondary device will revert to the
NDM state after a time delay (after the last
frame has been received).
MCP2140
DS21790A-page 51