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Methods of collection interfaces |
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| Release time:2013-05-22 Source:admin Reads: | |
| Early barcode scanners that used to read barcode labels, of all formats, almost universally used the then-common RS-232 serial interface. This was an electrically simple means of connection and the software to access it is also relatively simple, although needing to be written for specific computers and their serial ports. There are a few other less common interfaces. These were used in large EPOS systems with dedicated hardware, rather than attaching to existing commodity computers. In some of these interfaces, the scanning device returned a "raw" signal proportional to the intensities seen while scanning the barcode labels. This was then decoded by the host device. In some cases the scanning device would convert the symbology of the barcode to one that could be recognized by the host device, such as Code 39. With the popularity of the PC and its standard keyboard interface, it became ever easier to connect physical hardware to a PC and so there was commercial demand similarly to reduce the complexity of the associated software. "Keyboard wedge" hardware plugged between the PC and its normal keyboard, with characters from the barcode scanner appearing exactly as if they had been typed at the keyboard. This made the addition of simple barcode labels reading abilities to existing programs very easy, without any need to change them, although it did require some care by the user and could be restrictive in the content of the barcodes that could be handled. Later barcode readers began to use USB connectors rather than the keyboard port, as this became a more convenient hardware option. To retain the easy integration with existing programs, a device driver called a "software wedge" could be used, to emulate the keyboard-impersonating behaviour of the old "keyboard wedge" hardware. In many cases, a choice of USB interface types (HID, CDC) are provided. Some have Powered USB. |
