Datasheet
Section 16 USB Function Module (USB)
R01UH0309EJ0500 Rev. 5.00 Page 1011 of 1408
Sep 24, 2012
H8S/2456, H8S/2456R, H8S/2454 Group
16.7.3 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 the EPSTL register, and returns a stall handshake (1-1 in figure 16.20).
Once an internal status bit is set, it remains set until cleared by a Clear Feature command from the
host, without regard to the EPSTL register. After a bit is cleared by the Clear Feature command,
EPSTL is referenced (3-1 in figure 16.20). 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 16.20). To clear a stall, therefore,
the internal status bit must be cleared with a Clear Feature command (3-1 in figure 16.20). If set
by the application, EPSTL should also be cleared (2-1 in figure 16.20).
(1) Transition from normal operation to stall
(1-1)
(2) When transaction is performed when internal status bit is set, and Clear Feature is sent
(2-1)
STALL handshake
Transaction request
STALL handshake
(2-2)
Clear Feature command
(3) When Clear Feature is sent before transaction is performed
(3-1)
1. In case of USB
specification
violation, etc., USB
function module
stalls endpoint
automatically
1. Transmission of
STALL handshake
1. Internal status bit
cleared to 0
2. EPSTL not changed
1. EPSTL cleared to 0
by application
2. IN/OUT token
received from host
3. Internal status bit
already set to 1
4. EPSTL not
referenced
5. Internal status bit
not changed
Normal status restored
Internal status bit
0 → 1
EPSTL
0
Internal status bit
1
EPSTL
0
Internal status bit
1
EPSTL
0
Internal status bit
1 → 0
EPSTL
0
Stall status maintained
To (2-1) or (3-1)
Figure 16.20 Automatic Stall by USB Function Module