AT43USB320A_04 ATMEL [ATMEL Corporation], AT43USB320A_04 Datasheet - Page 70

• Manufacturer Part Number: AT43USB320A_04
• Description: Full-speed USB Microcontroller with an Embedded Hub
• Manufacturer: ATMEL [ATMEL Corporation]

Control Transfers at
Control Endpoint EP0
70
AT43USB320A
that the transaction has been completed successfully. Retries and data toggles are performed
automatically by the USB hardware. When the IN endpoint is not ready to send data, in the
case where the microcontroller has not filled the FIFO, it will automatically respond with a
NAK.
Similarly, an OUT endpoint will wait for an OUT token. When one is received, it will store the
data in the FIFO, completes the transaction and interrupt the microcontroller, which then reads
the FIFO and enables the endpoint for the next packet. If the FIFO is not cleared, the USB
hardware will responds with a NAK.
A detailed description of how USB transactions are handled is described in the following sec-
tions. First for a control endpoint and then for non-control endpoints.
The description given below is for the function control endpoint, but applies to the hub control
endpoint as well if the proper registers are used.
The following illustration describes the three possible types of control transfers – Control
Write, Control Read and No-data control:
Control
Write
Control
Read
No-data
Control
SETUP(0)
SETUP(0)
SETUP(0)
Setup
Stage
Setup
Stage
DATA0
DATA0
DATA0
DATA1(0)
OUT(1)
Status
DATA1
DATA1
Stage
IN(1)
IN(1)
OUT(0)
IN(0)
Stage
DATA0
DATA0
Data
DATAn
DATA1(0)
…
…
OUT(0/1)
DATA0/1
DATA0/1
IN(0/1)
Data packet with PID’s
data toggle bit equal to n
Zero length DATA1 packet
Legend:
DATA1(0)
DATA1(0)
Status
OUT(1)
Stage
IN(1)
IN(1)
1443E–USB–4/04