Rainbow Electronics AT89C5122 - Manual (Page 110)

110
AT8xC5122/23
4202E–SCR–06/06
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
register. The RXSETUP, TXRDY, TXCMPL, RXOUTB0 and RXOUTB1 bits must be first
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.