Microchip Technology AC164139 データシート
2010 Microchip Technology Inc.
DS39969B-page 253
PIC24FJ256DA210 FAMILY
18.6.2
HOST NEGOTIATION PROTOCOL
(HNP)
(HNP)
In USB OTG applications, a Dual Role Device (DRD) is
a device that is capable of being either a host or a
peripheral. Any OTG DRD must support Host
Negotiation Protocol (HNP).
HNP allows an OTG B-device to temporarily become
the USB host. The A-device must first enable the
B-device to follow HNP. Refer to the “On-The-Go
Supplement to the USB 2.0 Specification” for more
information regarding HNP. HNP may only be initiated
at full speed.
After being enabled for HNP by the A-device, the
B-device requests being the host any time that the USB
link is in suspend state, by simply indicating a discon-
nect. This can be done in software by clearing
DPPULUP and DMPULUP. When the A-device detects
the disconnect condition (via the URSTIF (U1IR<0>)
interrupt), the A-device may allow the B-device to take
over as host. The A-device does this by signaling con-
nect as a full-speed function. Software may accomplish
this by setting DPPULUP.
If the A-device responds instead with resume signaling,
the A-device remains as host. When the B-device
detects the connect condition (via ATTACHIF
(U1IR<6>), the B-device becomes host. The B-device
drives Reset signaling prior to using the bus.
a device that is capable of being either a host or a
peripheral. Any OTG DRD must support Host
Negotiation Protocol (HNP).
HNP allows an OTG B-device to temporarily become
the USB host. The A-device must first enable the
B-device to follow HNP. Refer to the “On-The-Go
Supplement to the USB 2.0 Specification” for more
information regarding HNP. HNP may only be initiated
at full speed.
After being enabled for HNP by the A-device, the
B-device requests being the host any time that the USB
link is in suspend state, by simply indicating a discon-
nect. This can be done in software by clearing
DPPULUP and DMPULUP. When the A-device detects
the disconnect condition (via the URSTIF (U1IR<0>)
interrupt), the A-device may allow the B-device to take
over as host. The A-device does this by signaling con-
nect as a full-speed function. Software may accomplish
this by setting DPPULUP.
If the A-device responds instead with resume signaling,
the A-device remains as host. When the B-device
detects the connect condition (via ATTACHIF
(U1IR<6>), the B-device becomes host. The B-device
drives Reset signaling prior to using the bus.
When the B-device has finished in its role as host, it
stops all bus activity and turns on its D+ pull-up resistor
by setting DPPULUP. When the A-device detects a
suspend condition (Idle for 3 ms), the A-device turns off
its D+ pull-up. The A-device may also power-down the
V
stops all bus activity and turns on its D+ pull-up resistor
by setting DPPULUP. When the A-device detects a
suspend condition (Idle for 3 ms), the A-device turns off
its D+ pull-up. The A-device may also power-down the
V
BUS
supply to end the session. When the A-device
detects the connect condition (via ATTACHIF), the
A-device resumes host operation and drives Reset
signaling.
A-device resumes host operation and drives Reset
signaling.
18.6.3
EXTERNAL V
BUS
COMPARATORS
The external V
BUS
comparator option is enabled by set-
ting the UVCMPDIS bit (U1CNFG2<1>). This disables
the internal V
the internal V
BUS
comparators, removing the need to
attach V
BUS
to the microcontroller’s V
BUS
pin.
The external comparator interface uses either the
V
V
CMPST
1 and V
CMPST
2 pins, or the V
BUSVLD
,
SESSVLD and SESSEND pins, based upon the setting
of the UVCMPSEL bit (U1CNFG2<5>). These pins are
digital inputs and should be set in the following patterns
(see Table 18-3), based on the current level of the V
of the UVCMPSEL bit (U1CNFG2<5>). These pins are
digital inputs and should be set in the following patterns
(see Table 18-3), based on the current level of the V
BUS
voltage.
TABLE 18-3:
EXTERNAL V
BUS
COMPARATOR STATES
If UVCMPSEL = 0
V
CMPST
1
V
CMPST
2
Bus Condition
0
0
V
BUS
< VB_SESS_END
1
0
VB_SESS_END < V
BUS
< VA_SESS_VLD
0
1
VA_SESS_VLD < V
BUS
< VA_VBUS_VLD
1
1
V
BUS
> VBUS_VLD
If UVCMPSEL = 1
V
BUSVLD
SESSVLD
SESSEND
Bus Condition
0
0
1
V
BUS
< VB_SESS_END
0
0
0
VB_SESS_END < V
BUS
< VA_SESS_VLD
0
1
0
VA_SESS_VLD < V
BUS
< VA_VBUS_VLD
1
1
0
V
BUS
> VBUS_VLD