Figure 6.18-5 Data Out Transfer - Nuvoton ISD94124BYI Technical Reference Manual

Alternatively, when USB host wants to transmit data to the OUT endpoint in the device controller,
hardware will buffer these data to the specified endpoint buffer. After this transaction is completed,
hardware will record the data length in specified USBD_MXPLDx register and de-assert the internal
signal "Out_Rdy". This will avoid hardware accepting next transaction until user moves out the
current data in the related endpoint buffer. Once users have processed this transaction, the
specified USBD_MXPLDx register needs to be written by firmware to assert the signal "Out_Rdy"
again to accept the next transaction.
USB
OUT PID
Bus Packets
USB_IRQ
Out_Rdy
Sep 9, 2019
ISD94100 Series Technical Reference Manual
Read Data from Buffer
Data 0/1 ACK PID OUT PID
Set by Hardware Clear by Firmware
Clear by Hardware

Figure 6.18-5 Data Out Transfer

Page 838 of 928
NAK PID OUT PID Data 0/1
Set by writing
Clear by Hardware
USBD_MXPLDx register
ACK PID
Rev1.09