Measurement Collection Specialists
USB & RS-232 Connections
The purpose of this page is to provide a better understanding of USB and serial ports, and to dispel some myths about serial communications and the rumored demise of the serial ports. Let's take a look at a couple of the more common myths that some of our customers believe to be fact.
Myth #1: Serial Ports are
Many of the new computers that are shipped today are shipped with multiple USB ports but do not contain RS-232 serial ports. Many people think that since new computers do not have any built-in RS-232 ports, that devices (scales, interfaces, etc.) with RS-232 outputs are obsolete. Since some new computers do not contain a parallel printer port, does that mean printers are obsolete? Neither of these ports (serial or parallel) are obsolete, just the method of connecting these devices to your PC has changed.
RS-232 communication is a very cost effective way to handle communications at rates from a few hundred characters per second (cps) to rates in excess of 100,000 cps. The shift to eliminate the RS-232 port and provide multiple USB ports is actually a very good solution, since it gives you greater flexibility as to the types of devices you can connect to your PC. You can easily connect devices such as parallel printers, digital cameras, scanners, gage interfaces, etc. to the USB ports on your computer. If you need an RS-232 port on your PC, you can purchase an RS-232 to USB adapter cable for as little as $35 and convert a USB port to a single or multiple RS-232 port.
The ability to communicate via an RS-232 link is built into many of the microcontrollers available in the marketplace today. These microcontrollers provide the processing and communications functions in devices such as scales, torque wrenches, gage interfaces, etc. The cost to designer to add RS-232 communications to these devices is just pennies.
Myth #2: Most Application
Software Communicates Directly to USB Port?
Windows applications normally do not communicate directly with any hardware, but rather to software drivers. If you have connected a USB to Serial cable to one of the USB ports on your computer and your application opens that serial port, your application has no idea, and it doesn't care, whether the serial port is located on the motherboard or connected to a Serial to USB cable. The drivers within Windows take care of how the communication actually occurs. The same kind of thing happens if you have a USB printer. Your application doesn't know and doesn't care whether that printer is connected to a standard 25-pin parallel port or to a USB port. Your application prints to Windows and the Windows drivers take care of the communications with the appropriate hardware.
What Does Your SPC/DAQ
If you take a look at the setup portion of your application that will be reading data from external devices, typically what you are going to see is that you can connect to anything as long as it looks like a serial port. The setup dialog will allow you to select COM1, COM2, etc. and it will also ask you to specify baud rate and communications parameters (i.e., 9600-N-8-1). What you will not see is something that allows you to select a USB port to communicate with.
In summary, your application is looking for a serial port. It doesn't care whether this serial port is hard wired into the motherboard or is a serial port created through a USB connection.
The MicroRidge Solution
MicroRidge provides one interface that has a direct USB connection, which is the USB version of the GageWay SM. This was done because it has a built-in cable and is more convenient to plug this cable directly into a USB port on your computer.
The other MicroRidge interfaces all contain an RS-232 serial port. These interfaces are connected to the computer via a "communications cable." This communications cable can be a standard DB9 RS-232 extension cable or a Serial to USB cable. By providing a serial port on the interface, it gives the customer the flexibility to connect to both serial and USB ports, and also allows the customer to chain the interfaces using a GageWay5 or a GageWay6.
Remember that whether you connect MicroRidge interfaces to a 9-pin serial port or a USB port, the connection looks like a serial port to your application.
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Revised September 30, 2014