EID Reader Connections & Comparison - CattleTags.com
All electronic ID readers have a com port (serial port) that cattle software uses to communicate with the reader.
There are 3 cases in which an electronic ID reader is connected to your computer. In all 3 cases, the EID reader is assigned a com port and your software does not differentiate between the type of connection in which the reader is connected to the computer. In other words, the method for accessing the EID readers is the same regardless of the type of connection.
Serial cable plugged into a serial port - Readers which have an RS-232 connection, also known as a serial port, are plugged directly into the serial port connection on the back of the computer. Your computer is configured so that a serial port has a com port. For example, serial port 1 on your computer may correspond to com port 1 on your computer. NOTE: plugging an EID reader into different serial ports into the computer may cause the reader to use different com ports.
Serial cable plugged into a USB adapter - Computers that do not have serial ports can utilize RS-232 EID readers with a serial to USB adapter. This adapter has a serial connection on one end and a USB connection on the other end and is plugged into a USB port on the computer. This USB adapter is assigned a com port by Windows. In some cases, plugging the USB adapter into different USB ports on the same computer can lead to the EID reader using a different com port.
Bluetooth - Bluetooth readers are connected wirelessly to the computer. Bluetooth drivers (software) assign the Bluetooth device a com port. Bluetooth can very easily lead to different com ports being used by the reader. Another issue with the Bluetooth technology is that the reader can become disconnected from the computer such as when the reader goes into standby (sleep). In addition, your software's connection to the com port can be blocked if another program is already accessing the com port.