![]() ![]() Given everything else works fine, this code should return the device handle successfully. hComPort = CreateFile("COM9", GENERIC_READ | GENERIC_WRITE, 0, 0, OPEN_EXISTING, 0, 0) The code below works just fine as long as the port number is COM9 or below. When successful, the CreatFile() function will return a handle to the port that can be used for further interaction with the port. Usually Serial ports can be opened for communication on Windows by passing the device name such as COM2 to the CreateFile() function (or the equivalent method offered by your language/library to open a port). This poses a challenge when trying to write your own program to control or communicate with these devices. It is easy to see how fast the COM port numbers can grow beyond COM9. But since they are reserved by Windows, when a new device is attached to the PC, Windows cannot reuse those names for the new device. The serial ports that are grayed out in the image below represent devices that are not attached to the PC the moment. The situation has gotten even worse by the fact that Windows tend to reserve port names and that becomes unusable for new devices. Now it is easy to go have a COM port on your machine that goes beyond COM9. But as USB CDC devices became very popular, it has become very easy to attach a lot of devices to a single machine. Even then, the chances of having more than nine serial ports on a single machine was slim unless you had a bunch of those cards installed on the same machine. You could have more if you had a PCI or ISA Serial Port expansion card installed. In the olden days, PCs and laptops used to be equipped with one or two serial ports. An example of such a device is in the image below as shown in Windows Device Manager. This also allows for a range of products such as Numato Lab’s USB GPIO and USB Relay modules to use USB but still have the ease of use Serial interface offers. USB specification defines a class ( Communication Devices Class) for using USB transport and infrastructure to emulate serial port interface thus legacy applications can continue operate even when the hardware uses USB. Although PCs and Laptops don’t come with built in serial ports anymore, serial port interface emulated over USB is very popular among DIYers/hackers and with certain products. Make doc # (optional) builds _this_ documentation.Serial ports were used in a verity of applications reliably for a very long time now. Make test # (optional) builds the example and tests, and runs the tests. Once you have checked out the source code from you can enter the directory and build the software. Once you have gathered the dependencies, you need to checkout the software from :
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