The ’HCT646 devices consist of bus-transceiver circuits with 3-state outputs, D-type flip-flops, and control circuitry arranged for multiplexed transmission of data directly from the input bus or from the internal registers. Data on the A or B bus is clocked into the registers on the low-to-high transition of the appropriate clock (CLKAB or CLKBA) input. Figure 1 illustrates the four fundamental bus-management functions that can be performed with the ’HCT646 devices.

Output-enable (OE)\ and direction-control (DIR) inputs control the transceiver functions. In the transceiver mode, data present at the high-impedance port can be stored in either or both registers.

The select-control (SAB and SBA) inputs can multiplex stored and real-time (transparent mode) data. DIR determines which bus receives data when OE\ is active (low). In the isolation mode (OE\ high), A data can be stored in one register and/or B data can be stored in the other register.

When an output function is disabled, the input function still is enabled and can be used to store data. Only one of the two buses, A or B, can be driven at a time.

To ensure the high-impedance state during power up or power down, OE\ should be tied to V_CC through a pullup resistor; the minimum value of the resistor is determined by the current-sinking capability of the driver.

• Operating Voltage Range of 4.5 V to 5.5 V
• Low Power Consumption, 80-μA Max ICC
• Typical tpd = 12 ns
• ±6-mA Output Drive at 5 V
• Low Input Current of 1 μA Max
• Inputs Are TTL-Voltage Compatible
• Independent Registers for A and B Buses
• Multiplexed Real-Time and Stored Data
• True Data Paths
• High-Current 3-State Outputs Can Drive Up To 15 LSTTL Loads

• IOL (Max) (mA)
• 6
• IOH (Max) (mA)
• -6
• Technology Family
• HCT
• Rating
• Catalog
• Operating temperature range (C)
• -40 to 85

SN74HCT646的完整型号有：SN74HCT646DW，以下是这些产品的关键参数及官网采购报价：

SN74HCT646DW，工作温度：-40 to 85，封装：SOIC (DW)-24，包装数量MPQ：25个，MSL 等级/回流焊峰值温度：Level-1-260C-UNLIM，引脚镀层/焊球材料：NIPDAU，TI官网SN74HCT646DW的批量USD价格：.593（1000+）

14-24-LOGIC-EVM — 支持 14 到 24 引脚 PW、DB、D、DW、NS、DYY 和 DGV 封装的通用逻辑 EVM

该 EVM 设计用于支持采用 14 至 24 引脚 D、DW、DB、NS、PW、DYY 或 DGV 封装的任何逻辑器件。