TUSB3200CPAH datasheet(27/93 Pages) TI

27 / 93 page

2–11

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 interrupt 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, the possibility

exists for data packets to be received and written to both the X and Y buffer before the MCU

responds to the endpoint interrupt. In this case, by 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.

2.2.7.2.2 Interrupt In Transaction

The steps to be followed for an interrupt in transaction are as follows:

MCU initializes one of the in endpoints as an in interrupt 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.

NOTE: In double buffer mode for interrupt in 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 read the data

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

buffer.

2.2.7.3 Bulk Transfers

The TUSB3200 supports bulk data transfers both to and from the host PC. Devices that need to send or receive a

large amount of data without a suitable bandwidth should use the bulk transfer type. In endpoints 1 through 7 and

out endpoints 1 through 7 can all be configured as bulk endpoints.

TUSB3200CPAH Datasheet(PDF) 27 Page - Texas Instruments