Packaging information
| Package | Pins CDIP (J) | 24 |
| Operating temperature range (°C) -55 to 125 |
| Package qty | Carrier 15 | TUBE |
Features for the CD54HC646
- 2-V to 6-V VCC Operation (CD54HC646)
- 4.5-V to 5.5-V VCC Operation (CD74HCT646)
- Wide Operating Temperature Range of –55°C to 125°C
- Balanced Propagation Delays and Transition Times
- Standard Outputs Drive Up To 15 LS-TTL Loads
- Significant Power Reduction Compared to LS-TTL Logic ICs
- Inputs Are TTL-Voltage Compatible (CD74HCT646)
- Independent Registers for A and B Buses
- Multiplexed Real-Time and Stored Data
- True Data Paths
Description for the CD54HC646
The CD54HC646 and CD74HCT646 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 these 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 VCC through a pullup resistor; the minimum value of the resistor is determined by the current-sinking capability of the driver.