Browse Prior Art Database

Tri State Driver Protection

IP.com Disclosure Number: IPCOM000050801D
Original Publication Date: 1982-Dec-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 2 page(s) / 39K

Publishing Venue

IBM

Related People

Millham, EH: AUTHOR

Abstract

When tri-state drivers are connected in multiples to a single bus and two or more of the drivers are switched to opposing logical states, one or more drivers may be damaged.

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Tri State Driver Protection

When tri-state drivers are connected in multiples to a single bus and two or more of the drivers are switched to opposing logical states, one or more drivers may be damaged.

It is well known that the use of tri-state drivers has advantages for the designer of computing and data processing systems with bus architectures. Prior to this invention, the use of such drivers has been inhibited due to the fact that system failures or programming errors can cause the drivers to be destroyed.

This invention teaches a method whereby the tri-state driver provides current of sufficient magnitude to charge the bus capacitance during the signal transition, then reduces the current available to a value sufficient only to drive the DC load on the bus.

The minimal DC current available will not be sufficient to damage the output device even if another driver on the same line is turned on to the opposing logic level. The high current output device is protected since, if some other driver connected to the bus is turned on to the opposing logic level, the current limit of the driver will prevent damage to the driver being switched.

Referring to the figure, devices 1 through 8 comprise the standard non- inverting tri-state driver. Devices 7 and 8 are designed to have smaller than normal dimensions, so as to limit the current available from these devices. Devices 9 through 15 comprise the line charge circuit for positive transitions, while devices 16 through 22 comprise the line charg...