AT89C5131A-RDTUM datasheet(129/188 Pages) ATMEL

129 / 188 page

129

4337K–USB–04/08

AT89C5130A/31A-M

21.4.4

Bulk/Interrupt IN Transactions in Ping-pong Mode

Figure 21-10. Bulk/Interrupt IN Transactions in Ping-pong Mode

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

packets.

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

STAX 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

will 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

will 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 (TXCMPL) 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 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

AT89C5131A-RDTUM Datasheet(PDF) 129 Page - ATMEL Corporation

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