TUSB3200CPAH datasheet(28/93 Pages) TI

28 / 93 page

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2.2.7.3.1 Bulk Out Transaction

The steps to be followed for a bulk out transaction are as follows:

MCU initializes one of the out endpoints as an out bulk endpoint by programming the appropriate USB

endpoint configuration block. 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.

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

is received without an error then the UBM will write the data to the endpoint buffer, update the data count

value, toggle the toggle bit, set the NACK bit to a 1, return an ACK handshake to the host PC and assert

the endpoint interrupt.

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

first needs to obtain the data count value. After reading the data packet, the MCU should clear the interrupt

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

If the NACK bit is set to a 1 when the data packet is received, the UBM simply returns a NAK handshake

to the host PC. If the STALL bit is set to a 1 when the data packet is received, the UBM simply returns a

STALL handshake to the host PC. If a CRC or bit stuff error occurs when the data packet is received, then

no handshake is returned to the host PC.

NOTE: In double buffer mode for bulk out transactions, the UBM selects between the X and

Y buffer based on the value of the toggle bit. If the toggle bit is a 0, the UBM will write the data

packet to the X buffer. If the toggle bit is a 1, the UBM will write the data packet to the Y buffer.

When a data packet is received, the MCU could determine which buffer contains the data

packet by reading the toggle bit. However, when using double buffer mode, data packets may

be received and written to both the X and Y buffer before the MCU responds to the endpoint

interrupt. In this case, simply using the toggle bit to determine which buffer contains the data

packet would not work. Hence, in double buffer mode, the MCU should read the X buffer NACK

bit, the Y buffer NACK bit, and the toggle bit to determine the status of the buffers.

2.2.7.3.2 Bulk In Transaction

The steps to be followed for a bulk in transaction are as follows:

MCU initializes one of the in endpoints as an in bulk endpoint by programming the appropriate USB endpoint

configuration block. 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 setting the NACK

bit.

The data packet to be sent to the host PC is written to the buffer by the MCU. The MCU also updates the

data count value then clears the NACK bit to a 0 to enable the data packet to be sent to the host PC.

The host PC sends an in token packet addressed to the in endpoint. After receiving the in token, the UBM

transmits the data packet to the host PC. If the data packet is received without errors by the host PC, then

an ACK handshake is returned. The UBM will then toggle the toggle bit, set the NACK bit to a 1 and assert

the endpoint interrupt.

The MCU services the interrupt and prepares to send the next data packet to the host PC.

If the NACK bit is set to a 1 when the in token packet is received, the UBM simply returns a NAK handshake

to the host PC. If the STALL bit is set to a 1 when the In token packet is received, the UBM simply returns

a STALL handshake to the host PC. If no handshake packet is received from the host PC, then the UBM

prepares to retransmit the same data packet again.

TUSB3200CPAH 数据表(PDF) 28 Page - Texas Instruments

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