The 'GTL16923 devices are 18-bit registered bus transceivers that provide LVTTL-to-GTL/GTL+ and GTL/GTL+-to-LVTTL signal-level translation. They are partitioned as two 9-bit transceivers with individual output-enable controls and contain D-type flip-flops for temporary storage of data flowing in either direction. The devices provide 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 output edge control (OECTM). The user has the flexibility of using these devices 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. All inputs can be driven from either 3.3-V or 5-V devices which allows use in a mixed 3.3-V/5-V system environment. VREF is the reference input voltage for the B port. Data flow in each direction is controlled by the output-enable (OEAB and OEBA) and clock (CLKAB and CLKBA) inputs. The clock-enable (CEAB and CEBA) inputs are used to enable or disable the clock for all 18 bits at a time. However, OEAB and OEBA are designed to control each 9-bit transceiver independently, which makes the device more versatile.