AT83SND1CXXX-ROTIL datasheet(89/212 Pages) ATMEL

89 / 212 page

4109J–8051–10/06

AT8xC51SND1C

All USB retry mechanisms are automatically managed by the USB controller.

14.4.4

Bulk/Interrupt IN Transactions in Ping-pong Mode

Figure 14-12. Bulk/Interrupt IN transactions in Ping-pong mode

An endpoint should be first enabled and configured before being able to send Bulk or Interrupt

packets.

The firmware should fill the FIFO bank 0 with the data to be sent and set the TXRDY bit in the

UEPSTAX register to allow the USB controller to send the data stored in FIFO at the next IN

request concerning the endpoint. The FIFO banks are automatically switched, and the firmware

can immediately write into the endpoint FIFO bank 1.

When the IN packet concerning the bank 0 has been sent and acknowledged by the Host, the

TXCMPL bit is set by the USB controller. This triggers a USB interrupt if enabled. The firmware

should clear the TXCMPL bit before filling the endpoint FIFO bank 0 with new data. The FIFO

banks are then automatically switched.

When the IN packet concerning the bank 1 has been sent and acknowledged by the Host, the

TXCMPL bit is set by the USB controller. This triggers a USB interrupt if enabled. The firmware

should clear the TXCMPL bit before filling the endpoint FIFO bank 1 with new data.

The bank switch is performed by the USB controller each time the TXRDY bit is set by the firm-

ware. Until the TXRDY bit has been set by the firmware for an endpoint bank, the USB controller

will answer a NAK handshake for each IN requests concerning this bank.

Note that in the example above, the firmware clears the Transmit Complete bit (TXCBulk-out-

MPL) before setting the Transmit Ready bit (TXRDY). This is done in order to avoid the firmware

to clear at the same time the TXCMPL bit for for bank 0 and the bank 1.

DATA0 (n Bytes)

ACK

HOST

UFI

C51

Endpoint FIFO bank 0 - Write Byte 1

NACK

TXCMPL

Endpoint FIFO bank 0 - Write Byte 2

Endpoint FIFO bank 0 - Write Byte n

Set TXRDY

Endpoint FIFO bank 1 - Write Byte 1

Endpoint FIFO bank 1 - Write Byte 2

Endpoint FIFO bank 1 - Write Byte m

Set TXRDY

DATA1 (m Bytes)

ACK

Endpoint FIFO bank 0 - Write Byte 1

Endpoint FIFO bank 0 - Write Byte 2

Endpoint FIFO bank 0 - Write Byte p

Set TXRDY

Clear TXCMPL

DATA0 (p Bytes)

ACK

TXCMPL

Clear TXCMPL

Endpoint FIFO bank 1 - Write Byte 1

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