Diodes Incorporated
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Invisible Logic is What We Want to See

By Johnny Lu, PTC Marketing Director


Why logic makes sense

Widespread in use, standard logic devices are often the preferred way to conjoin parts of a circuit where reliable connections are required, or even when there’s a need to overcome a design challenge within a system.

In short, logic makes sense. Sometimes, adding a standard logic function can make all the difference between a good circuit and a great circuit, especially if it compensates for that dreaded design oversight. However, the obvious problem with this is that adding any extra device can lead to a delay between input and output. If this propagation delay is significant, adding a standard logic device can easily create an unwelcome bottleneck in the system.

While no designer would expect instantaneous switching from one logical state to another (low to high or vice versa), every effort must be made to keep any gate delay to an absolute minimum. The impact of adding a standard logic device to any system should not be noticed: ‘invisible logic’ is what we need to see.


Port expanders, the logical solution

The solution is the humble I/O port expander. Unsung heroes of sorts, general-purpose input-output (GPIO) expanders represent a perfect example of how logic can be used well. Capable of monitoring and controlling a range of incoming and outgoing digital peripheral signals, port expanders offer a straightforward solution to the problems designers can experience when trying to add more I/O to a product or system.

GPIO port expanders may not make the headlines but they have proved to be essential tools for designers of digital cameras, GPS systems, industrial PCs, rack servers, base stations, multi-function printers, point-of-sale (POS) systems, TVs, tablets, smartphones, and a host of other products and applications.

Of course, while port expanders illustrate how logic can extend the capability of an existing circuit with minimal design effort, it is vital that designers choose their expanders wisely for the job they have in mind. As we established, port expanders should operate as if they were not there. If the wrong type is selected, the propagation delay designers are trying to avoid will become a real possibility.

With years of experience developing port expanders (especially 1-to-4 port expanders and 1-to-8 port units) for a range of sectors, Diodes Incorporated understands how these essential tools should be applied for maximum gain.


Speed is of the essence

To this end, GPIO expanders from the company are available with an I2C bus interface and 2 to 48 I/Os. Extras on some models in the extensive range include an additional INT (interrupt) output and/or RESET input signals. The output is used to inform the microcontroller if any input state has changed, while the RESET input enables the device to return to its default state without the need to power down.

Not only do I/O expanders from Diodes Incorporated deliver that sought after “invisible” logic by ensuring a virtually undetectable propagation delay, but they are faster than any product of their kind on the market today.  

Designers now have an off-the-shelf solution to issues they face when adding standard logic functions to their circuit designs and no longer have to worry how adding devices can have on the time between input and output. Invisible logic is here for all to see.

Further information and technical details on the full range of GPIO expanders from Diodes Incorporated can be found here.