The SN74GTL1655 is a high-drive (100 mA), low-output-impedance (12 ) 16-bit UBT™ transceiver that provides LVTTL-to-GTL/GTL+ and GTL/GTL+-to-LVTTL signal-level translation. This device is partitioned as two 8-bit transceivers and combines D-type flip-flops and D-type latches to allow for transparent, latched, and clocked modes of data transfer similar to the '16501 function. This device provides an interface between cards operating at LVTTL logic levels and a backplane operating at GTL/GTL+ signal levels. Higher-speed operation is a direct result of the reduced output swing (<1 V), reduced input threshold levels, and OEC™ circuitry. The high drive is suitable for driving double-terminated low-impedance backplanes using incident-wave switching. The user has the flexibility of using this device at either GTL (VTT = 1.2 V and VREF = 0.8 V) or the preferred higher noise margin GTL+ (VTT = 1.5 V and VREF = 1 V) signal levels. GTL+ is the Texas Instruments derivative of the Gunning Transceiver Logic (GTL) JEDEC standard JESD 8-3. The B port normally operates at GTL or GTL+ signal levels, while the A-port and control inputs are compatible with LVTTL logic levels but are not 5-V tolerant. VREF is the reference input voltage for the B port. This device is uniquely partitioned as two 8-bit transceivers with individual latch timing and output signals, but with a common clock and output enable inputs for both transceiver words. Data flow for each word is determined by the respective latch enables (LEAB and LEBA), output enables (OEAB and OEBA), and clock (CLK). The output enables (1OEAB, 1OEBA, 2OEAB, and 2OEBA) control byte 1 and byte 2 data for the A-to-B and B-to-A directions, respectively. For A-to-B data flow, the devices operate in the transparent mode when LEAB is high. When LEAB transitions low, the A data is latched independent of CLK high or low. If LEAB is low, the A data is registered on the CLK low-to-high transition. When OEAB is low, the outputs are active. With OEAB high, the outputs are in the high-impedance state.