ST STM32G0 1 Series Reference Manual page 1301

RM0444 Universal serial bus full-speed host/device interface (USB)
Table 227. Transmission status encoding (continued)
STATTX[1:0] Meaning
NAK:
Device mode: the endpoint is NAKed and all transmission requests result in a
10
NAK handshake.
Host mode: this indicates that the device has NAKed the transmission request.
11 VALID: this endpoint/channel is enabled for transmission.
RM0444 Rev 5 1301/1390
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