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74GTL1655 16-BIT LVTTL TO GTL/GTL +
Universal Bus Transceiver with Live Insertion

74GTL1655 Datasheet

The rapidly growing internet and tele-communications structures are constantly calling for faster and faster data transmission equipment. Technologies such as Asynchronous Transfer Mode (ATM) require high-performance backplane to connect the various modules in a system, and the backplane bus is driven by transceivers that must be able to support high frequency operation in order to increase bandwidth. The Gunning Transceiver Logic devices are reduced voltage swing transceivers between cards operating at LVTTL logic levels and GTL signal levels, designed for high-speed backplane bus applications. High speed operation is achieved through the reduced output voltage swing and the reduced high-level input threshold voltage provided by a differential amplifier input solution for safe detection of logic levels. ST offers a 16-bit, high-drive (100mA), low output impedance LVTTL to GTL/GTL+ universal bus transceiver in a TSSOP64 package. This device combines D-type Latches and D-type Flip-Flops, for different operation modes.

 



74GTL1655 live insertion: precharge feature
 

Features
b Translates between LVTTL and GTL/GTL+ signal levels;
b Combines D-type latches and D-type flip-flops for transparent, latched or clocked mode;
b Reduced voltage swing;
b High drive capability: IOL=100mA;
b Power-off disables outputs permitting live insertion;
b High-impedance state during power up and power down;
b B port biasing networks precondition the connector and PC trace to the GTL high level voltage;
b Edge rate control input configures the B port output rise and fall times;
b Bus hold feature (A port);
b High-speed switching noise minimized by distributed Vcc and GND pin configuration;
b TSSOP64 package;
b Direct replacement of TI’s SN74GTL1655.

Operating Mode Control
The function of the component is controlled and changed by the control inputs OE (disables both ports simultaneously), OEAB and OEBA (data flow direction), LEAB, and LEBA (latched mode enable). Three operating modes can be selected:
b Transparent mode: bidirectional bus driver;
b Level sensitive storage (latch) mode: bidirectional latch;
b Edge triggered storage (flip-flop) mode: bidirectional edge triggered register.

Applications
This GTL device has been especially designed to operate with heavily loaded backplane applications and fast bus systems.
Live Insertion
The live insertion feature allows insertion or removal of a board on the backplane without limitations, restrictions or requirements of additional circuitry concerning backplane power and signaling:
b 1) By limiting the current flowing from the bus when the device supply goes to zero, insertion or removal of the board without powering the host system down is possible.
b 2) At the same time, the host system does not need to suspend signaling, as a high-impedance state is ensured during power up or power down.
b 3) By precharging the GTL I/Os to a high level just before insertion/removal gives a true live insertion capability to this device.

Bus system evolution


 

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