MCP2140AT-ISLASHSS datasheet(53/60 Pages) MICROCHIP

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DS22050A-page 53

MCP2140A

C.1.2

IrLAP

The IrLAP protocol provides:

• Management of communication processes on the

link between devices

• A device-to-device connection for the reliable,

ordered transfer of data

• Device discover procedures

• Hidden node handling. 115.2 kbaud

Figure C-3 identifies the key parts and hierarchy of the

IrDA protocols. The bottom layer is the Physical layer,

IrPHY. This is the part that converts the serial data to

and from pulses of IR light. IR transceivers can’t

transmit and receive at the same time. The receiver

has to wait for the transmitter to finish sending. This is

sometimes referred to as a “Half-Duplex” connection.

The IR Link Access Protocol (IrLAP) provides the

structure for packets (or “frames”) of data to emulate

data that would normally be free to stream back and

forth.

FIGURE C-3:

IrDA STANDARD PROTOCOL

LAYERS

Figure C-4 shows how the IrLAP frame is organized.

The frame is preceded by some number of Beginning

of Frame characters (BOFs). The value of the BOF is

generally 0xC0, but 0xFF may be used if the last BOF

character is a 0xC0. The purpose of multiple BOFs is to

give the other station some warning that a frame is

coming.

The IrLAP frame begins with an address byte (“A”

field), then a control byte (“C” field). The control byte is

used to differentiate between different types of frames

and is also used to count frames. Frames can carry

status, data or commands. The IrLAP protocol has a

command syntax of it’s own. These commands are part

of the control byte. Lastly, IrLAP frames carry data.

This data is the information (or “I”) field. The integrity of

the frame is ensured with a 16-bit CRC, referred to as

the Frame Check Sequence (FCS). The 16-bit CRC

value is transmitted LSB first. The end of the frame is

marked with an EOF character, which is always a

0xC1. The frame structure described here is used for

all versions of IrDA protocols used for serial wire

replacement for speeds up to 115.2 kbaud.

FIGURE C-4:

IrLAP FRAME

In addition to defining the frame structure, IrLAP

provides the “housekeeping” functions of opening,

closing and maintaining connections. The critical

parameters that determine the performance of the link

are part of this function. These parameters control how

many BOFs are used, identify the speed of the link,

how fast either party may change from receiving to

transmitting, etc. IrLAP has the responsibility of

negotiating these parameters to the highest common

set so that both sides can communicate as quickly and

reliably as possible.

Note:

Not supported by MCP2140A.

Host O.S. or Application

IrCOMM

IrLAP

IrPHY

Protocols

resident in

MCP2140A

IR pulses

transmitted

and

received

IrLMP

–

IAS

Note 1: The

MCP2140A

only

supports

communication baud rate of 9600 baud.

2: Another IrDA standard that is entering

into general usage is IR Object Exchange

(IrOBEX). This standard is not used for

serial connection emulation.

3: IrDA communication standards faster

than 115.2 kbaud use a different CRC

method and physical layer.

X BOFs BOF A C

FCS

EOF

(1+N) of C0h payload

bytes C1h

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