SN74LS646 - Octal bus transceivers and registers

These devices consist of bus transceiver circuits with 3-state or open-collector 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 will be clocked into the registers on the low-to-high transition of the appropriate clock pin (CAB or CBA). The following examples demonstrate the four fundamental bus-management functions that can be performed with the octal bus transceivers and registers.

Enable (G\) and direction (DIR) pins are provided to control the transceiver functions. In the transceiver mode, data present at the high-impedance port may be stored in either register or in both. The select controls (SAB and SBA) can multiplex stored and real-time (transparent mode) data. The direction control determines which bus will receive data when enable G\ is active (low). In the isolation mode (control G\ high), A data may be stored in one register and/or B data may be stored in the other register.

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

The SN54' family is characterized for operation over the full military temperature range of –55°C to 125°C. The SN74' family is characterized for operation from 0° to 70°C.

• Independent Registers for A and B Buses
• Multiplexed Real-Time and Stored Data
• Choice of True or Inverting Data Paths
• Choice of 3-State or Open-Collector Outputs
• Included Among the Package Options Are Compact 24-pin 300-mil-Wide Plastic and Ceramic DIPs, Ceramic Chip Carriers, and Plastic "Small Outline" Packages
• Dependable Texas Instruments Quality and Reliability