USS-820FD
USB Device Controller
Data Sheet, Rev. 1
August 2004
Firmware Resume Sequence
The USS-820FD indicates that the resume sequence is
complete by setting the SSR.RESUME register bit, and
possibly causing an interrupt. When firmware is
prepared for the application to return to normal opera-
tion, it must reset the SSR.RESUME register bit to
allow detection of any subsequent suspend events.
Suspend and Resume Behavior
(continued)
Firmware Suspend Initiate
(continued)
While the USS-820FD is suspended, its internal regis-
ters may still be read, presumably only in self-powered
devices. The interface timing for such reads is different
from register reads during operational mode, and is
specified in the Register Timing Characteristics
section. Register writes must not be attempted while
the USS-820FD is suspended, with the possible excep-
tion of the SCR.SRESET bit (see the SCR.SRESET
description for details). Certain register reads during
the nonsuspended state can cause USS-820FD device
register states to change. These reads are described in
the Register Reads with Side Effects section. These
register reads must not be attempted while the USS-
820FD is suspended.
Special Suspend Considerations for Bus-
Powered Devices
In order to meet the USB current requirements while
suspended, care must be exercised to guarantee that
all board signals connected to the USS-820FD are at
their proper state. Voltages on USS-820FD input pins
must be guaranteed to be outside the switching
threshold region (i.e., either a valid CMOS logic 1 or 0).
Pins that are connected to external, powered-off
components must not be driven high.
If an external oscillator is used as the clock source for
the USS-820FD, it will most likely need to be turned off
by the USS-820FD SUSPN output pin in order to meet
the USB suspend current requirement. When the oscil-
lator is turned back on after a resume (when the
SUSPN pin deasserts) and is stabilizing (a period that
must not exceed t
OSC
as specified in Table 47), its
output clock must not have a frequency greater than
12 MHz. As a result, during this stabilization period, the
oscillator output must not provide more than
84,000 clocks.
The following list describes the expected (or required,
as noted) values on the USS-820FD pins for devices
which turn power off to external components during
suspend. Such devices must have SSR.SUSPPO = 1
to cause D[7:0], IRQN, and SOFN to be 3-stated during
suspend. They must also have MCSR.BDFEAT = 0
while suspended in order to guarantee that USBR and
DSA are 3-stated. These register settings avoid the
possibility of driving a logic 1 into a powered-off compo-
nent, which could result in excessive power consump-
tion and possible component damage.
External logic refers to components external to the
USS-820FD.
Note:
Board signals which are connected to powered-
off components will most likely be naturally
pulled to logic 0 by the powered-off component.
■
Hardware Resume Detect/Initiate
Wake-up can be initiated by either the host or the appli-
cation. A host-signaled wake-up (global resume) is
indicated when the host drives a K state on the USB
bus. A remote wake-up is initiated by the application by
asserting the USS-820FD RWUPN input pin. The USS-
820FD can also be awakened by firmware writing a 1
to SCR.SRESET if MCSR.FEAT = 1 (see
SCR.SRESET description for details). In these cases,
the USS-820FD will initiate a wake-up sequence as
described in the next section.
Hardware Resume Sequence
The USS-820FD starts a wake-up sequence by asyn-
chronously re-enabling its internal oscillator and PLL
and deasserting the SUSPN output pin. Once the inter-
nally generated clocks are stable (a period of 6 ms to
15 ms), then it enables clocks to the entire chip and
sets the SSR.RESUME register bit, which causes an
interrupt if SCRATCH.IE_RESUME register bit = 1. The
USS-820FD will require up to 15 ms to resume func-
tionality after a wake-up sequence is initiated. If the
wake-up was a remote wake-up, the USS-820FD will
then drive wake-up signaling (K) on the USB for 12 ms.
The USS-820FD requires a minimum of 7 ms from the
time a remote wake-up is initiated to the time it can
begin transmitting resume signaling upstream. This
guarantees adherence to the USB specification for
tWTRSM of 5 ms.
A[4:0], IOCSN, RDN, WRN: Input-only pins. Their
value will be determined by external logic, and must
be a logic 0 or 1 to avoid current draw in the USS-
820FD.
44
Agere Systems Inc.
AGERE [ AGERE SYSTEMS ]
