SDLS144D April 1985 – October 2016 SN54LS240 , SN54LS241 , SN54LS244 , SN54S240 , SN54S241 , SN54S244 , SN74LS240 , SN74LS241 , SN74LS244 , SN74S240 , SN74S241 , SN74S244
- 1 Features
- 2 Applications
- 3 Description
- 4 Revision History
- 5 Pin Configuration and Functions
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6 Specifications
- 6.1 Absolute Maximum Ratings
- 6.2 ESD Ratings
- 6.3 Recommended Operating Conditions
- 6.4 Thermal Information
- 6.5 Electrical Characteristics - SNx4LS24x
- 6.6 Electrical Characteristics - SNx4S24x
- 6.7 Switching Characteristics - SNx4LS24x
- 6.8 Switching Characteristics - SNx4S24x
- 6.9 Typical Characteristics
- 7 Parameter Measurement Information
- 8 Detailed Description
- 9 Application and Implementation
- 10Power Supply Recommendations
- 11Layout
- 12Device and Documentation Support
- 13Mechanical, Packaging, and Orderable Information
11 Layout
11.1 Layout Guidelines
When using multiple bit logic devices, inputs must not be left floating. In many applications, some channels of the SNx4LS24x, SNx4S24x are unused, and thus must be terminated properly. Because each transceiver channel pin can be either an input or an output, they must be treated as both when being terminated. Ground or VCC (whichever is more convenient) can be used to terminate unused inputs; however, each unused channel should be terminated to the same logic level on both the A and Y side. For example, in Figure 27 unused channels are terminated correctly with both sides connected to the same voltage, while channel 8 is terminated incorrectly with each side being tied to a different voltage. The G input is also unused in this example, and is terminated directly to ground to permanently enable all outputs.
11.2 Layout Example
Figure 27. Example Demonstrating How to Terminate Unused Inputs and Channels of a Transceiver