Rainbow Electronics AT89C5131 - Manual (Page 123)

123
AT89C5131
4136A–USB–03/03
Bulk/Interrupt IN Transactions
in Ping-pong Mode 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.
IN
DATA0 (n Bytes)
ACK
HOST UFI C51
Endpoint FIFO Bank 0 - Write Byte 1
IN
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
IN
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
IN
DATA0 (p Bytes)
ACK
TXCMPL
Clear TXCMPL
Endpoint FIFO Bank 1 - Write Byte 1