Automatic Serial Data Collection

As more and more devices come equipped with some type of communication for data collection and monitoring, the amount of data that can be collected by a PC in a system is astounding. A problem arises, however, when multiple instruments or devices need access to the PC through the serial port, but only one port is available.

There are multiple options for expanding the capability of a port that was designed to communicate with only one device. You can add a separate serial port for each RS-232 device that you need to talk to. By adding serial ports, multiple devices can have their own dedicated port, often concurrently and at high speeds. The drawback is that separate serial ports may be expensive and require some effort to configure. There is also a practical limit on resources available inside the PC to allocate to Serial Ports.

Multiple devices can be tied together by converting the signal at each point to a multi-drop bus, like RS-485. This allows up to 32 devices on a single network without repeaters. The devices can also be connected up to 4000 feet away from the PC. The disadvantage is that each device must have its own unique address. Also, some protocol needs to be established to prevent more than one device at a time from sending data to the PC. Usually this is done by having the PC poll each device individually. This does not lend itself well to devices that send their data automatically, without being requested.

Using the 232BSS4 buffered Smart Switch is an excellent way to collect data from multiple devices utilizing RS-232 serial ports. Up to four instruments, card readers, or time clocks can be directly connected to the 232BSS4, providing access through a single serial port on your PC.

If you have more than four devices that are sending data, more than one 232BSS4 can be cascaded, allowing more ports to be added. The 232BSS4 buffers data from all ports at once, making it well suited for devices that will send a fixed amount of data at sporadic intervals, such as measurement instruments, security access card readers, barcode scanners, or time clocks. Below is an explanation of how best to utilize the 232BSS4 to connect these devices to your PC.>