Chapter 16
tion data. For example, a telephone device might use an audio interface to send
and receive voice data.
The example descriptors include a data class interface with two bulk endpoint
addresses. In the data class interface descriptor, bInterfaceNumber identifies the
interface as interface 01h. The bInterfaceClass field identifies the interface as a
CDC data class interface. The interface has a bulk IN endpoint for sending
data to the host and a bulk OUT endpoint for receiving data from the host.
The wMaxPacketSize field specifies the maximum number of bytes an endpoint
can transfer in one transaction’s data packet. Endpoints in full-speed devices
typically use the maximum allowed values of 64. Endpoints in high-speed
devices must use 512. A transfer larger than wMaxPacketSize bytes uses multi-
ple transactions. A short packet is a data packet that contains less than wMax-Table 16-5: A Functional descriptor consists of a Header functional descriptor
followed by one or more function-specific descriptors.
" 1
+!
00h Header
01h Call Management
02h Abstract Control Management
03h Direct Line Control Management
04h Telephone Ringer
05h Telephone Call and Line State Reporting Capabilities
06h Union
07h Country Selection
08h Telephone Operational Modes
09h USB Terminal
0Ah Network Channel Terminal
0Bh Protocol Unit
0Ch Extension Unit
0Dh Multi-channel Management
0Eh CAPI Control Management
0Fh Ethernet Networking
10h ATM Networking
11h–18h WMC Functional Descriptors
19h–FFh Reserved