TAS1020B datasheet(28/114 Pages) TI

28 / 114 page

2–14

2.2.7

USB Transfers

The TAS1020B device supports all USB data transfer types: control, bulk, interrupt, and isochronous. In accordance

with the USB specification, endpoint zero is reserved for the control endpoint and is bidirectional. In addition to the

control endpoint, the TAS1020B is capable of supporting up to 7 IN endpoints and 7 OUT endpoints. These additional

endpoints can be configured as bulk, interrupt, or isochronous endpoints.

2.2.7.1 Control Transfers

Control transfers are used for configuration, command, and status communication between the host PC and the

TAS1020B device. Control transfers to the TAS1020B device use IN endpoint 0 and OUT endpoint 0. The three types

of control transfers are control write, control write with no data stage, and control reads.

2.2.7.1.1 Control Write Transfer (Out Transfer)

The host PC uses a control write transfer to write data to the USB function. A control write transfer always consists

of a setup stage transaction and an IN status stage, and can optionally contain one or more data stage transactions

between the setup and status transactions. If the data to be transferred can be contained in the two byte value field

of the setup transaction data packet, no data stage transaction is required. If the control information requires the

transfer of more than two bytes of data, a control write transfer with data stage transactions will be required. The steps

followed for a control write transfer are:

Initialization Stage:

MCU initializes IN endpoint 0 and OUT endpoint 0 by programming the appropriate USB endpoint

configuration blocks. This entails programming the buffer size and buffer base address, selecting the buffer

mode, enabling the endpoint interrupt, initializing the TOGGLE bit, enabling the endpoint, and clearing the

NACK bit for both IN endpoint 0 and OUT endpoint 0.

Setup Stage Transaction:

The host PC sends a setup token followed by the setup data packet addressed to OUT endpoint 0. If the

data is received without an error, the USB Buffer Manager (UBM) writes the data to the setup data packet

buffer, sets the setup stage transaction (SETUP) bit to a 1 in the USB status register, returns an ACK

handshake to the host PC, and asserts the setup stage transaction interrupt. Note that as long as the setup

stage transaction (SETUP) bit is set to a 1, the UBM returns a NACK handshake for any data stage or status

stage transactions regardless of the endpoint 0 NACK or STALL bit values.

The MCU services the interrupt, reads the setup data packet from the buffer, and decodes the command.

If the command is not supported or valid, the MCU should set the STALL bit in the OUT endpoint 0

configuration byte and the IN endpoint 0 configuration byte before clearing the setup stage transaction

(SETUP) bit. This causes the device to return a STALL handshake for any data stage or status stage

transactions. If the command decoded is supported, the MCU clears the interrupt, which automatically

clears the setup stage transaction bit. The MCU also sets the TOGGLE bit in the OUT endpoint 0

configuration byte to a 1. For control write transfers, the PID used by the host for the first OUT data packet

is a DATA1 PID and the TOGGLE bit must match.

Optional Data Stage Transaction:

The host PC sends an out token packet followed by a data packet addressed to OUT endpoint 0. If the data

packet is received without errors the UBM writes the data to the endpoint buffer, updates the data count

value, toggles the TOGGLE bit, sets the NACK bit to a 1, returns an ACK handshake to the host PC, and

asserts the endpoint interrupt.

The MCU services the interrupt and reads the data packet from the buffer. To read the data packet, the MCU

first must obtain the data count value. After reading the data packet, the MCU must clear the interrupt and

clear the NACK bit to allow the reception of the next data packet from the host PC.

TAS1020B Datasheet(PDF) 28 Page - Texas Instruments

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