AT89C5122 ATMEL [ATMEL Corporation], AT89C5122 Datasheet - Page 106

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

Bulk/Interrupt IN Transactions
in Ping-Pong Mode
106
AT8xC5122/23
Figure 58. Bulk / Interrupt IN transactions in Ping-Pong mode
An endpoint will be first enabled and configured before being able to send Bulk or Inter-
rupt packets.
The firmware will 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 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 firmware. 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 (TXC-
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 bank 0 and the bank 1.
The firmware will never write more bytes than supported by the endpoint FIFO.
HOST
IN
IN
IN
IN
ACK
ACK
ACK
DATA0 (n Bytes)
DATA1 (m Bytes)
DATA0 (p Bytes)
NACK
UFI
TXCMPL
TXCMPL
Endpoint FIFO Bank 0 - Write Byte 1
Endpoint FIFO Bank 0 - Write Byte 2
Endpoint FIFO Bank 0 - Write Byte n
Endpoint FIFO Bank 1 - Write Byte 1
Endpoint FIFO Bank 1 - Write Byte 2
Endpoint FIFO Bank 1 - Write Byte m
Endpoint FIFO Bank 0 - Write Byte 1
Endpoint FIFO Bank 0 - Write Byte 2
Endpoint FIFO Bank 0 - Write Byte p
Endpoint FIFO Bank 1 - Write Byte 1
C51
Clear TXCMPL
Clear TXCMPL
Set TXRDY
Set TXRDY
Set TXRDY
4202D–SCR–06/05