AT43USB325E-AC Atmel, AT43USB325E-AC Datasheet - Page 63

• Manufacturer Part Number: AT43USB325E-AC
• Description: IC USB KEYBOARD CTRLR HUB 64LQFP
• Manufacturer: Atmel
• Series: AVR®r

Specifications of AT43USB325E-AC

• Applications: Keyboard Controller
• Core Processor: AVR
• Program Memory Type: SRAM (16 kB)
• Controller Series: AT43USB
• Ram Size: 512 x 8
• Interface: SPI, 3-Wire Serial
• Number Of I /o: 42
• Voltage - Supply: 4.4 V ~ 5.25 V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 64-LQFP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

8. Programming the USB Module
8.1
3355C–USB–4/05
USB Function
The USB hardware consists of two devices, hub and function, each with their own device
address and endpoints. Its operation is controlled through a set of memory mapped registers.
The exact configuration of the USB device is defined by the software and it can be programmed
to operate as a compound device, or as a hub only or as a function only. The hub has the
required control and interrupt endpoints. The number of external downstream ports is program-
mable from 0 to 2. The DP and DM pins of the unused port(s) must be connected to ground. The
USB function has one control endpoint and 2 programmable endpoints. All the endpoints have
their own 8-byte FIFOs. If the hub is disabled, one extra endpoint becomes available to the
function.
The USB function hardware is designed to operate in the single packet mode and to manage the
USB protocol layer. It consists of a Serial Interface Engine (SIE), endpoint FIFOs and a Function
Interface Unit (FIU). The SIE performs the following tasks: USB signaling detection/generation,
data serialization/de-serialization, data encoding/decoding, bit stuffing and un-stuffing,
clock/data separation, and CRC generation/checking. It also decodes and manages all packet
data types and packet fields.
The endpoint FIFO buffers the data to be sent out or data received. The FIU manages the flow of
data between the SIE, FIFO and the internal microcontroller bus. It controls the FIFO and moni-
tors the status of the transactions and interfaces to the CPU. It initiates interrupts and acts upon
commands sent by the firmware.
The USB function hardware of the AT43USB325 makes the physical interface and the protocol
layer transparent to the user. To start the process, the firmware must first enable the endpoints
and which place them in receive mode by default. The device address by default is address 0.
The USB function hardware then waits for a setup token from the host. When a valid setup token
is received, it automatically stores the data packet in endpoint 0 FIFO and responds with an
ACK. It then notifies the microcontroller through an interrupt. The microcontroller reads the FIFO
and parses the request.
Transactions for the non-control endpoints are even simpler. Once the endpoint is enabled, it
waits for an IN or an OUT token depending whether it is programmed as an IN or OUT endpoint.
For example, if it is an IN endpoint, the microcontroller simply loads the data into the endpoint's
FIFO and sets a bit in the control and status register. The USB hardware will assemble the data
in a USB packet and waits for an IN token. When it receives one, it automatically responds by
transmitting the data packet and completes the transaction by waiting for the host's ACK. When
one is received, the USB hardware will signal the microcontroller that the transaction has been
completed successfully. Retries and data toggles are performed automatically by the USB hard-
ware. 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 hard-
ware 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.
AT43USB325
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