L-USS820D-DB LSI, L-USS820D-DB Datasheet - Page 43
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L-USS820D-DB
Manufacturer Part Number
L-USS820D-DB
Description
Manufacturer
LSI
Datasheet
1.L-USS820D-DB.pdf
(56 pages)
Specifications of L-USS820D-DB
Operating Temperature (min)
-20C
Operating Temperature Classification
Commercial
Operating Temperature (max)
85C
Rad Hardened
No
Lead Free Status / RoHS Status
Compliant
Data Sheet, Rev. 7
September 2004
SUSPEND and RESUME Behavior
(continued)
During a SUSPEND/RESUME sequence, the following
sequence of events occurs:
1. Hardware SUSPEND Detect: The USS-820D
2. Firmware SUSPEND Initiate: Firmware reacts to the
3. Hardware RESUME Detect/Initiate: Some time later
4. Hardware RESUME Sequence: When the
5. Firmware RESUME Sequence: Firmware reacts to
The following sections describe each of these steps in
more detail.
Hardware SUSPEND Detect
The USS-820D detects a USB SUSPEND condition if a
J state persists on the bus for at least 3 ms. When this
SUSPEND condition is detected, hardware sets the
SSR.SUSPEND register status bit and, if IE_SUSP = 1,
causes an interrupt.
SUSPEND detection may be blocked by firmware by
setting the SSR.SUSPDIS register bit to 1.
SSR.SUSPDIS should only be set for test purposes,
never in a running system.
Firmware SUSPEND Initiate
When firmware detects that a SUSPEND request from
the host has been detected, it must prepare itself, and
any other application components for which it is
responsible, for SUSPEND mode. For bus-powered
devices, this will normally require turning off power to
application components or placing them in low-power
mode. When firmware is finished preparing for a device
SUSPEND, it should check the SSR.SUSPEND
register status bit once more. If this status bit has
RESET, firmware should abort the SUSPEND
sequence, since the host has already awakened the
device. This will only happen if firmware is too slow in
responding to the SUSPEND detect. If the status bit is
still SET, firmware should proceed with the SUSPEND
sequence. This second check of the status bit guaran-
tees that the device will see wake-up signaling of suffi-
cient length from the host.
Agere Systems Inc.
detects a SUSPEND request from the host on USB
and notifies firmware.
pending SUSPEND request and suspends the
device.
a RESUME is initiated, either by the host or the
application.
RESUME is complete, the USS-820D notifies firm-
ware.
the RESUME and completes any required actions.
To SUSPEND the USS-820D, firmware must set the
SSR.SUSPEND register control bit to 1, and then reset
the bit to 0. This action causes to the USS-820D to
immediately enter SUSPEND mode.
In order to guarantee correct behavior when resuming,
firmware must not attempt any register reads until at
least three tRDREC periods have elapsed since reset-
ting the SSR.SUSPEND register control bit.
Since firmware must have the PEND register bit set
when modifying the SSR.SUSPEND register bit, and
since registers cannot be written while the USS-820D is
suspended, firmware must remember to reset the
PEND register bit after the USS-820D resumes.
Since the SSR.SUSPEND register status bit will remain
SET while the USS-820D is suspended, a pending
SUSPEND interrupt will remain until the USS-820D
resumes. For this reason, firmware may wish to reset
the SCR.IE_SUSP bit before suspending the USS-
820D.
In order to meet the USB specification’s current draw
limit for suspended devices, the USS-820D must turn
off its internal clocks. This occurs when the
SSR.SUSPEND register control bit is reset by firmware
as described above and is indicated by the USS-820D
SUSPN output pin being asserted. While in SUSPEND
mode, the USS-820D must remain powered, but the
USS-820D’s power consumption will be reduced to
almost zero and will remain in this state until a wake-up
is signaled.
Self-powered devices will most likely not need to turn
off power to other application components during
SUSPEND. This is indicated to the USS-820D by the
SSR.SUSPPO register bit = 0, which should be written
by firmware at device initialization time. In such an envi-
ronment, during SUSPEND, the USS-820D outputs
and inputs continue to be driven by the USS-820D and
the application, respectively. In addition, the USS-820D
bidirectional pins are tristated in the USS-820D and
driven to 0 or 1 by the application.
Bus-powered devices will most likely need to turn off
power to other application components during
SUSPEND. This is indicated to the USS-820D by the
SSR.SUSPPO register bit = 1, which should be written
by firmware at device initialization time. Such devices
can be implemented so that the USS-820D SUSPN
output pin controls power to other application compo-
nents. Issues which must be considered by bus-
powered devices are discussed in the Special
SUSPEND Considerations for Bus-Powered Devices
section.
USB Device Controller
USS-820D
43