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.