Serial Port Complete - Latest Microcontroller projects

Chapter 16

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Abstract control model devices support up to three notifications:

Each notification begins with an 8-byte header:

The device typically returns notifications on the interface’s interrupt IN end-

point. The host doesn’t request specific notifications. Instead, the host periodi-

cally issues IN token packets to the endpoint, and the endpoint returns

notifications as available. The endpoint descriptor’s bInterval field specifies the

maximum latency between IN token packets. An endpoint that has no notifica-

tion to return should return NAK on receiving an IN token packet.

Devices that support the abstract control model must support the

RESPONSE_AVAILABLE notification. However, if the device is a generic

COM-port device that doesn’t connect to a modem that supports AT com-

mands, the device will have no need for this notification and will return NAK

on every IN token packet to the notification endpoint.

The SERIAL_STATE notification is optional but recommended for devices

with asynchronous serial interfaces. The notification sends the states of RS-232

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NETWORK_CONNECTION 0x00 Network or modem

connection status.

Optional.

RESPONSE_AVAILABLE 0x01 Requests the host to issue a

GET_ENCAPSULATED_

RESPONSE request.

Required but not used if

AT commands aren’t

implemented.

SERIAL_STATE 0x20 State of CD, DSR, Break,

and RI

Optional but

recommended for devices

that support these signals.

1 !    

bmRequestType 1 0x0A

bNotification 1 Notification code

wValue 2 Notification-specific data

wIndex 2 bInterfaceNumber

wLength 2 Number of data bytes to follow (zero or more)