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Preliminary Data Sheet, Rev. 5 USS-720
Instant USB
September 1999 USB-to-
IEEE
1284 Bridge
Lucent Technologies Inc. 5-5
13
Overview
The USS-720 creates a bridge between one USB port
and one
IEEE
1284 enhanced parallel port. Internally,
the USS-720 contains an integrated USB transceiver, a
USB device controller (UDC) core, an
IEEE
1284 core,
integrated
IEEE
1284 buffers, storage for USB configu-
ration data, data buffers, and control logic to tie the
blocks together. The USS-720 also contains an
onboard oscillator, PLL, and reset block for single-chip
operation.
In use, the USB port of the USS-720 is connected via a
USB cable to a host computer or the downstream port
of a USB hub. Host software sends commands and
data to the USS-720 and receives status and data from
the USS-720 using the USB protocol.
The
IEEE
1284 enhanced parallel port of the device is
connected to a peripheral device. If the peripheral is
IEEE
1284 compatible, then the associated features
and communication modes can be used. The USS-720
provides both automatic and manual operation of the
IEEE
1284 port.
USB Port
The USB port on the USS-720 is electrically and logi-
cally compliant with the
USB Specification Revision
1.0
.
Device Descriptor, Configurations, and Inter-
faces
Supported Descriptors
■ Device.
■ Configuration.
■ Interface. The USS-720 device supports one inter-
face with three alternate settings.
— Interface 0, alternate settings 0 and 1 are
compliant with the
USB Device Class Definition
for Printing Devices, Release Candidate 1.0
.
— Interface 0, alternate setting 2 is a vendor-specific
interface.
■ Endpoint. The USS-720 supports the following end-
points:
— Control endpoint. Accessible as endpoint 0 in all
three alternate interface settings.
— Bulk Out endpoint. Accessible as endpoint 1 in all
three alternate interface settings.
— Bulk In endpoint. Accessible as endpoint 2 in
alternate interface settings 1 and 2.
— Interrupt endpoint. Accessible as endpoint 3 in
alternate interface setting 2.
■ String.
Descriptor Locations
Descriptor data is supplied from an external ROM or
other device. The USS-720 provides support for
93CS56 and 93CS66 EEPROM interfaces.
(Note: Substitution EEPROM components must be pin
and functional compatible with the 93CS56L/66L.
93C56L/66L, 93CS46L, and 93C46L EEPROM parts
will not function correctly with the USS-720.) The for-
mat for the externally supplied descriptor data requires
that the descriptors loaded be preceded by the total
length of the descriptor to be returned. In the case of
the device descriptor, this value would be 0x12, which
is redundant since the descriptor returned is always
0x12 bytes long; the first byte of the descriptor would
also be 0x12. The length of the configuration descrip-
tor, however, is not the same as the first byte of that
descriptor, since the configuration descriptor and all
associated interface and endpoint descriptors are
returned as a whole.
The USS-720 also contains a set of device, configura-
tion, interface, and endpoint descriptors that may be
used in development and prototyping. Retrieval of the
onboard descriptors will occur if no external descriptor
data is supplied.