AT90USB646 datasheet(270/456 Pages) ATMEL

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270

7593L–AVR–09/12

AT90USB64/128

23.14.1

Overview

The Endpoint must be configured first.

The TXINI bit is set by hardware when the current bank becomes free. This triggers an interrupt

if the TXINE bit is set. The FIFOCON bit is set at the same time. The CPU writes into the FIFO

and clears the FIFOCON bit to allow the USB controller to send the data. If the IN Endpoint is

composed of multiple banks, this also switches to the next data bank. The TXINI and FIFOCON

bits are automatically updated by hardware regarding the status of the next bank.

TXINI shall always be cleared before clearing FIFOCON.

The RWAL bit always reflects the state of the current bank. This bit is set if the firmware can

write data to the bank, and cleared by hardware when the bank is full.

Figure 23-7. Example with 1 and 2 IN data bank.

23.14.2

Detailed description

The data are written by the CPU, following the next flow:

• When the bank is empty, an endpoint interrupt (EPINTx) is triggered, if enabled (TXINE set)

and TXINI is set. The CPU can also poll TXINI or FIFOCON, depending the software

architecture choice

• The CPU acknowledges the interrupt by clearing TXINI

•The CPU can write the data into the current bank (write in UEDATX)

• The CPU can free the bank by clearing FIFOCON when all the data are written, that is:

– after “N” write into UEDATX

– as soon as RWAL is cleared by hardware

DATA

(bank 0)

ACK

TXINI

FIFOCON

write data from CPU

BANK 0

Example with 2 IN data banks

DATA

(bank 0)

ACK

TXINI

FIFOCON

write data from CPU

BANK 0

DATA

(bank 1)

ACK

write data from CPU

BANK 0

write data from CPU

BANK 1

write data from CPU

BANK0

NAK

AT90USB646 Datasheet(PDF) 270 Page - ATMEL Corporation

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