How an RS232 connector soldered to an USB cable?
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A simple cable is not enough to connect RS232 devices to a computer with only USB ports. There are however converter modules and cables that can be successfully used to connect RS232 devices to computers via an USB port. These adapters and cables contain electronics, and the success rate depends on the capabilities of this electronics and the device driver software that is shipped with the converter to communicate with these electronics over the USB bus. Before buying your USB to RS232 converter, it is advised that you read this document first.
Differences from the application point of view
RS232 is a definition for serial communication on a 1:1 base. RS232 defines the interface layer, but not the application layer. To use RS232 in a specific situation, application specific software must be written on devices on both ends of the connecting RS232 cable. The developer is free to define the protocol used to communicate. RS232 ports can be either accessed directly by an application, or via a device driver in the operating system.
USB on the other hand is a bus system which allows more than one peripheral to be connected to a host computer via one USB port. Hubs can be used in the USB chain to extend the cable length and allow for even more devices to connect to the same USB port. The standard not only describes the physical properties of the interface, but also the protocols to be used. Because of the complex USB protocol requirements, communication with USB ports on a computer is always performed via a device driver.
It is easy to see where the problems arise. Developers have lots of freedom where it comes to defining RS232 communications and ports are often directly, or almost directly accessed in the application program. Settings like baudrate, databits, hardware software flow control can often be changed within the application. The USB interface does not give this flexib
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