Lucent Technologies USS-720 manual Filter Bypass Mode, High Drive Mode, Self-Powered Mode

Preliminary Data Sheet, Rev. 5	USS-720	Instant USB
September 1999	USB-to-IEEE	1284 Bridge

Filter Bypass Mode

For embedded applications, the USS-720 IEEE 1284 port can be operated in Filter Bypass Mode. This mode disables digital filtering of the parallel port signals into the USS-720, providing a performance improvement.

Note: Since digital filtering is disabled, the parallel port lines will be susceptible to noise. Do not use this mode when driving across a cable.

Filter Bypass Mode is enabled by connecting a 20 kΩ pull-down resistor to the SUSPEND line.

High Drive Mode

If desired (e.g., for embedded applications), the USS- 720 IEEE 1284 port can operate in High Drive Mode. In

this mode, all parallel port signals are constantly driven by 14 mA totem-pole drivers, rather than with the normal open-drain drivers. This eliminates the need for external pull-up resistors on the parallel port signals (and, if driving another chip on the same board, there is no need for the 24 Ω impedance matching resistors). High Drive Mode is enabled by connecting a 20 kΩ pull-down resistor to the SK line.

Self-Powered Mode

When using the USS-720 in a self-powered applica- tion, attach a 5 kΩ pull-up resistor to the CS line. This causes the correct self-powered status to be reported in response to a USB Get-Status command.

Absolute Maximum Ratings

Stresses in excess of the absolute maximum ratings can cause permanent damage to the device. These are abso- lute stress ratings only. Functional operation of the device is not implied at these or any other conditions in excess of those given in the operations sections of this data sheet. Exposure to absolute maximum ratings for extended periods can adversely affect device reliability.

Table 30. Absolute Maximum Ratings

Parameter	Symbol	Min	Max	Unit
Ambient Operating Temperature Range	TA	0	70	°C
Storage Temperature	Tstg	−40	125	°C
Voltage on Any Pin with Respect to Ground	VIN	VSS − 0.3	VDD + 0.3*	V

*Except for 5 V tolerant buffers where VIN max = VDD5 max + 0.3 V. VIN must never exceed VDD5 + 0.3 V at any time. VDD5 should be selected to satisfy this condition.

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