MCP2140-IP datasheet(51/58 Pages) MICROCHIP

51 / 58 page

 2003 Microchip Technology Inc.

Preliminary

DS21790A-page 51

MCP2140

C.2

Discovery Mode

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.

C.3

Normal Connect Mode (NCM)

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:

The MCP2140 is limited to a data rate of

9.6 kbaud.

Note:

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-IP датащи(PDF) 51 Page - Microchip Technology

MCP2140-IP датащи(HTML) 51 Page - Microchip Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58

датащи скачать

ссылки URL