AT89C5122D-RDRUM datasheet(108/208 Pages) ATMEL

108 / 208 page

108

AT83R5122, AT8xC5122/23

4202F–SCR–07/2008

Miscellaneous

USB Reset

The EORINT bit in the USBINT register is set by hardware when a End of Reset has

been detected on the USB bus. This triggers a USB interrupt if enabled. The USB con-

troller is still enabled, but all the USB registers are reset by hardware. The firmware

should clear the EORINT bit to allow the next USB reset detection.

STALL Handshake

This function is only available for Control, Bulk, and Interrupt endpoints.

The firmware has to set the STALLRQ bit in the UEPSTAX register to send a STALL

handshake at the next request of the Host on the endpoint selected with the UEPNUM

reset to 0. The bit STLCRC is set at 1 by the USB controller when a STALL has been

sent. This triggers an interrupt if enabled.

The firmware should clear the STALLRQ and STLCRC bits after each STALL sent.

The STALLRQ bit is cleared automatically by hardware when a valid SETUP PID is

received on a CONTROL type endpoint.

Start of Frame Detection

The SOFINT bit in the USBINT register is set when the USB controller detects a Start Of

Frame PID. This triggers an interrupt if enabled. The firmware should clear the SOFINT

bit to allow the next Start of Frame detection.

Frame Number

When receiving a Start of Frame, the frame number is automatically stored in the

UFNUML and UFNUMH registers. The CRCOK and CRCERR bits indicate if the CRC of

the last Start Of Frame is valid (CRCOK set at 1) or corrupt (CRCERR set at 1). The

UFNUML and UFNUMH registers are automatically updated when receiving a new Start

of Frame.

Data Toggle Bit

The Data Toggle bit is set by hardware when a DATA 0 packet is received and accepted

by the USB controller and cleared by hardware when a DATA 1 packet is received and

accepted by the USB controller. This bit is reset when the firmware resets the endpoint

FIFO using the UEPRST register.

For Control endpoints, each SETUP transaction starts with a DATA 0 and data toggling

is then used as for Bulk endpoints until the end of the Data stage (for a control write

transfer). The Status stage completes the data transfer with a DATA 1 (for a control read

transfer).

For Isochronous endpoints, the device firmware should ignore the data-toggle.

NAK Handshakes

When a NAK handshake is sent by the USB controller to a IN or OUT request from the

Host, the NAKIN or NAKOUT bit is set by hardware. This information can be used to

determine the direction of the communication during a Control transfer.

These bits are cleared by software.

AT89C5122D-RDRUM 数据表(PDF) 108 Page - ATMEL Corporation

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