If you need a new computer or a laptop with a built-in serial port, you are in trouble, especially when it comes to mobile computers. In almost all home or office environments, the old serial protocol was replaced by the Universal Serial Bus, the USB, so PC manufacturers stopped providing them as standard hardware.
But in the industrial world much equipment still needs the serial ports, the RS-232 or RS-422/485 interfaces, to communicate with each other. So, this situation creates a major gap between the personal or working computers and the industrial electronics.
A small USB history review
When introduced in 1995 by a seven company’s consortium, the USB technology was designed as an advanced way to connect computers with their peripherals and other components. This consortium, called the USB Implementers Forum Inc., included over time more than 1000 members, which helped the promotion and development of USB technology.
Before USB, to add peripherals to a computer system or network, you had to power it down first, install and expansion card, reboot the system and install the necessary drivers. With the USB technology, this whole process was radically streamlined. Users could add or remove peripherals and other Human Interface Devices without the need of rebooting, devices becoming hot swappable. The drivers were still needed, but you only had to install them once and there was no need of specialised internal cards anymore.
In fact, USB was a state of the art, an excellent expansion for any computer. Plus, combined with USB hubs, proper computer resources and proper wiring, a single USB port can sustain 127 devices. Before USB, the serial connection, the DB9, could only control one device, one equipment.
History can confirm the USB technology effectiveness and usefulness, but if you need to use older protocols, to keep your equipment functional throughout its useful life, you need to get your hands on a USB-to-serial convertor. But we will get to that a little bit later, because you’ll need the correct convertor for your equipment. And before going forward, you need to be able to identify it correctly.
Through the years, the USB technology had several revisions and USB’s naming conventions can be confusing at certain times. For example, USB 1.1 referred to Low Speed and Full Speed, USB 2.0 has added High Speed that is faster than Full Speed and on top of that, USB 3.0 has added SuperSpeed in the mix. So we will try to make this data more understandable to anyone:
|USB Speed||USB Protocol||Rate||Bi-Directional|
|Low Speed||USB 1.1, 2.0, 3.0||1.5 Mbps||Half Duplex||100 mA||X|
|Full Speed||USB 1.1, 2.0, 3.0||12 Mbps||Half Duplex||100 mA||X|
|High Speed||USB 2.0, 3.0||480 Mbps||Half Duplex||100 mA||X|
|SuperSpeed||USB 3.0||4.8 Gbps||Full Duplex||900 mA||Yes|
It is also important to know that every USB version is fully compatible with its predecessors, but it will not go faster than it. So if you have a USB 3.0 device plugged into a USB 1.1 port, it will work with the USB 1.1 speed. And the reverse is also true, so if you plug a USB 1.1 device into a USB 3.0 port, it will work with the USB 1.1 speed.
And to be able to identify your device capabilities:
Standard USB Logo – tells us the existence of the USB connection. This can be either version 1.1, 2.0 or 3.0
High-Speed USB Logo – indicates the presence of the USB 2.0 technology
SuperSpeed USB 3.0 Logo – now we have a 4.8 Gbit/s data rate. But these ports can come with high-power or low-power, providing 900 mA or 150 mA. This will affect the data rates, the battery charging specifications and the concurrent data transmission.
Also, the standard USB hardware is compatible with older USB ports and cables. The only exception is the USB 3.0 micro connectors that work only with SuperSpeed devices.
Serial to USB
Equipment that uses the serial connection can be connected to computers even with lacking appropriate ports. The converters mentioned earlier, the USB-to-Serial converters, act like a serial port expansion card. The only difference is that they use the USB interface, not the PCI slot or the PCI Express slot.
So when the USB-to-Serial converter is plugged into the USB port, its driver will open a serial COM port that can be used by software applications. This way, any legacy peripherals or equipment will remain entirely operational.
As an example, we can take the USB-to-Serial converter that connects to a 9-pin DB9, which can be used for RS-232 devices. But keep in mind that your operating system, baud rates, cable types, buffer rates, duplex capabilities and many other factors will vary a lot. And the same goes with the converters for RS-422 and RS-485 connections.
Because of these factors and differences, it is the utmost importance to know and understand the exact specifications needed for the conversion. Among these elements, the essential ones are:
1. The type of the serial protocol and the type of the device that handles it. We are referring to the RS-232, RS-422 and RS-485 serial protocols.
2. The needed transfer rate
3. If you need full-duplex or half-duplex
4. If you are dealing with the DB9 or DB25 male or female connectors
5. If your working environment is electrically noisy or if isolation is required to prevent damage to the host computer
6. The required voltage on the serial lines that will be required from the converter
7. If the converter be needed to be shared between multiple computers
8. Chose a stable platform as the chipset and the drivers are very important
To bridge the gap left in the market can be easy if you choose the right convertor for your equipment. With its help, you just have to plug the convertor into the computer’s USB port and connect your peripheral at the other end. Install the drivers and then hot swap elements or components as necessary. Also, to ensure maximum reliability, make sure that you purchase the best components, install stable drivers and stay in the ranges of the FTDI chipset.