Datasheet

94
32142D–06/2013
ATUC64/128/256L3/4U
Figure 8-6. Control Write
• Control read
Figure 8-7 on page 94 shows a control read transaction. The USBC has to manage the simulta-
neous write requests from the CPU and USB host.
Figure 8-7. Control Read
A NAK handshake is always generated as the first status stage command. The UESTAn.NAKINI
bit is set. It allows the user to know that the host aborts the IN data stage. As a consequence,
the user should stop processing the IN data stage and should prepare to receive the OUT status
stage by checking the UESTAn.RXOUTI bit.
The OUT retry is always ACKed. This OUT reception sets RXOUTI. Handle this with the follow-
ing software algorithm:
// process the IN data stage
set TXINI
wait for RXOUTI (rising) OR TXINI (falling)
if RXOUTI is high, then process the OUT status stage
if TXINI is low, then return to process the IN data stage
Once the OUT status stage has been received, the USBC waits for a SETUP request. The
SETUP request has priority over all other requests and will be ACKed.
SETUP
RXSTPI
RXOUTI
TXINI
USB Bus
HW SW
OUT
HW SW
OUT
HW SW
IN IN
NAK
SW
DATASETUP STATUS
SETUP
RXSTPI
RXOUTI
TXINI
USB Bus
HW SW
IN
HW SW
IN OUT OUT
NAK
SW
SW
HW
Wr Enable
HOST
Wr Enable
CPU
DATASETUP STATUS