Section 20 USB Function Module
Rev. 4.00 Sep. 14, 2005 Page 782 of 982
REJ09B0023-0400
20.6.2 Automatic Stall by USB Function Module
When a stall setting is made with the Set Feature command, or in the event of a USB specification
violation, the USB function module automatically sets the internal status bit for the relevant
endpoint without regard to USBEPSTL register, and returns a stall handshake (1-1 in
figure 20.14).
Once an internal status bit is set, it remains set until cleared by a Clear Feature command from the
host, without regard to USBEPSTL register. After a bit is cleared by the Clear Feature command,
USBEPSTL is referenced (3-1 in figure 20.14). The USB function module continues to return a
stall handshake while the internal status bit is set, since the internal status bit is set even if a
transaction is executed for the corresponding endpoint (2-1 and 2-2 in figure 20.14). To clear a
stall, therefore, the internal status bit must be cleared with a Clear Feature command (3-1 in figure
20.14). If set by the application, USBEPSTL should also be cleared (2-1 in figure 20.14).
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