AT89C5122 ATMEL [ATMEL Corporation], AT89C5122 Datasheet - Page 104

• Manufacturer Part Number: AT89C5122
• Description: MICROCONTROLLER WITH USB AND SMART CARD READER INTERFACES
• Manufacturer: ATMEL [ATMEL Corporation]

Bulk/Interrupt OUT
Transactions in Ping-Pong
Mode (Endpoints 6)
104
AT8xC5122/23
Figure 56. Bulk / Interrupt OUT Transactions in Ping-Pong Mode
An endpoint should be first enabled and configured before being able to receive Bulk or
Interrupt packets.
When a valid OUT packet is received on the endpoint bank 0, the RXOUTB0 bit is set by
the USB controller. This triggers an interrupt if enabled. The firmware has to select the
corresponding endpoint, store the number of data bytes by reading the UBYCTX regis-
ter. If the received packet is a ZLP (Zero Length Packet), the UBYCTX register value is
equal to 0 and no data has to be read.
When all the endpoint FIFO bytes have been read, the firmware should clear the
RXOUB0 bit to allow the USB controller to accept the next OUT packet on the endpoint
bank 0. This action switches the endpoint bank 0 and 1. Until the RXOUTB0 bit has
been cleared by the firmware, the USB controller will answer a NAK handshake for each
OUT requests on the bank 0 endpoint FIFO.
When a new valid OUT packet is received on the endpoint bank 1, the RXOUTB1 bit is
set by the USB controller. This triggers an interrupt if enabled. The firmware empties the
bank 1 endpoint FIFO before clearing the RXOUTB1 bit. Until the RXOUTB1 bit has
been cleared by the firmware, the USB controller will answer a NAK handshake for each
OUT requests on the bank 1 endpoint FIFO.
The RXOUTB0 and RXOUTB1 bits are alternatively set by the USB controller at each
new valid packet receipt.
The firmware has to clear one of these two bits after having read all the data FIFO to
allow a new valid packet to be stored in the corresponding bank.
A NAK handshake is sent by the USB controller only if the banks 0 and 1 has not been
released by the firmware.
OUT
OUT
OUT
HOST
DATA0 (n bytes)
DATA1 (m bytes)
DATA0 (p bytes)
ACK
ACK
ACK
UFI
RXOUTB0
RXOUTB1
RXOUTB0
Endpoint FIFO bank 0 - read byte 1
Endpoint FIFO bank 0 - read byte 2
Endpoint FIFO bank 0 - read byte n
Endpoint FIFO bank 1 - read byte 1
Endpoint FIFO bank 1 - read byte 2
Endpoint FIFO bank 1 - read byte m
Endpoint FIFO bank 0 - read byte 1
Endpoint FIFO bank 0 - read byte 2
Endpoint FIFO bank 0 - read byte p
Clear RXOUTB0
Clear RXOUTB1
Clear RXOUTB0
C51
4202D–SCR–06/05