MCP2140-I/SSRVB Microchip Technology, MCP2140-I/SSRVB Datasheet - Page 50

• Manufacturer Part Number: MCP2140-I/SSRVB
• Description: 9600 BAUD FIXED SPEED IRDA PROTOCOL HANDLER & BIT ENCODER/DECODER, -40C to +85C, 20-SSOP 208mil, TUBE
• Manufacturer: Microchip Technology

MCP2140
APPENDIX C: HOW DEVICES
When two devices implementing the IrDA standard fea-
ture establish a connection using the IrCOMM protocol,
the process is analogous to connecting two devices
with serial ports using a cable. This is referred to as a
“point-to-point” connection. This connection is limited
to half-duplex operation because the IR transceiver
cannot transmit and receive at the same time. The pur-
pose of the IrDA protocols is to allow this half-duplex
link to emulate, as much as possible, a full-duplex con-
nection. In general, this is done by dividing the data into
“packets”, or groups of data. These packets can then
be sent back and forth, when needed, without risk of
collision. The rules of how and when these packets are
sent constitute the IrDA protocols.
When a wired connection is used, the assumption is
made that both sides have the same communications
parameters and features. A wired connection has no
need to identify the other connector because it is
assumed that the connectors are properly connected.
In the IrDA standard, a connection process has been
defined to identify other IrDA compatible devices and
establish a communication link. There are three steps
that these two devices go through to make this
connection. They are:
• Normal Disconnect Mode (NDM)
• Discovery Mode
• Normal Connect Mode (NCM)
Figure C-1
C.1
When two IrDA standard compatible devices come into
range they must first recognize each other. The basis
of this process is that one device has some task to
accomplish and the other device has a resource
needed to accomplish this task. One device is referred
to as a Primary device and the other is referred to as a
Secondary device. This distinction between Primary
device and Secondary device is important. It is the
responsibility of the Primary device to provide the
mechanism to recognize other devices. So the Primary
device must first poll for nearby IrDA standard compat-
ible devices. During this polling, the default baud rate of
9600 baud is used by both devices.
For example, if you want to print from an IrDA equipped
laptop to an IrDA printer, utilizing the IrDA standard fea-
ture, you would first bring your laptop in range of the
printer. In this case, the laptop is the one that has
something to do and the printer has the resource to do
it. The laptop is called the Primary device and the
printer is the Secondary device. Some data-capable
cell phones have IrDA standard infrared ports. If you
used such a cell phone with a Personal Digital Assis-
DS21790A-page 50
Normal Disconnect Mode (NDM)
shows the connection sequence.
CONNECT
Preliminary
tant (PDA), the PDA that supports the IrDA standard
feature would be the Primary device and the cell phone
would be the Secondary device.
When a Primary device polls for another device, a
nearby Secondary device may respond. When a Sec-
ondary device responds, the two devices are defined to
be in the Normal Disconnect Mode (NDM) state. NDM
is established by the Primary device broadcasting a
packet and waiting for a response. These broadcast
packets are numbered. Usually 6 or 8 packets are sent.
The first packet is number 0, the last packet is usually
number 5 or 7. Once all the packets are sent, the Pri-
mary device sends an ID packet, which is not num-
bered.
The Secondary device waits for these packets and then
responds to one of the packets. The packet responds
to determines the “timeslot” to be used by the Second-
ary device. For example, if the Secondary device
responds after packet number 2, then the Secondary
device will use timeslot 2. If the Secondary device
responds after packet number 0, then the Secondary
device will use timeslot 0. This mechanism allows the
Primary device to recognize as many nearby devices
as there are timeslots. The Primary device will continue
to generate timeslots and the Secondary device should
continue to respond, even if there’s nothing to do.
Note 1: The MCP2140 can only be used to
2: The MCP2140 supports a system with
3: The MCP2140 always responds to packet
4: If another Secondary device is nearby,
implement a Secondary device.
only one Secondary device having exclu-
sive use of the IrDA standard infrared link
(known as “point-to-point” communica-
tion).
number 2. This means that the MCP2140
will always use timeslot 2.
the Primary device may fail to recognize
the MCP2140, or the Primary device may
not recognize either of the devices.
2003 Microchip Technology Inc.