CDC Introduction

USB has been around for a while and as an end user, we may be quite grateful that a high speed data protocol makes life that much easier. RS232 memory sticks ? That seems a bit absurd!

However, USB enables data storage and data transfer seamlessly using the same interface and at times the same medium. RS 232 however is a data transfer protocol and was used extensively in a multitude of applications from industry to control DC motors or even in data logging applications. Domestic applications included from modems, printers flatbed scanners and so on.

Owing to this, it’s supplanting by the USB incumbent mean that older or what we politely term ‘legacy’ systems can experience a disconnect. As USB became more popular, laptops specifically started to loose that RS232 (9 PIN) comport. If you are a technician in an industrial environment, this meant that a replacement laptop would not be able to connect to those legacy systems. Yup, a problem you would have been unable to work!
You could improvise by purchasing serial to RS232 adapters, but hey that is one extra piece of equipment to worry about and carry in your laptop bag.
Interestingly, the USB interface has a number of classes HID, Mass Storage and CDC; by classes these are the manner by which the data is transferred. Most of us have used HID in practice. HID or Human Interface Device: Key boards and mice make us of this protocol. This class can be used to transfer data, but it would also require that.
But the method would require the PC software to be rewritten if you had a PC to hardware system. If you wanted a seamless transfer while using USB then CDC would be your best option. This method allows for comport emulation, in other words even though a physical USB connection is in place it functions in software as if it were a standard RS232 COM PORT.
The advantage of this is that legacy systems may not need any upgrade or system changes they would carry on and continue to function as per normal.
Recently, Mikroe released an updated USB library which supports CDC and we will shortly demonstrate how this can be used to enable the Consurgo 28 to communicate as if it were a RS232 Comport.


Mikroe :  USB Library for Mikroe Compilers

Local : Consurgo

Wikipedia: USB CDC