Have you had difficulty using a USB to RS-232 adapter to connect your RS-232 device to a computer? If so, you are not alone. Our customers frequently encounter issues with these adapters. In this article, I’ll briefly discuss the origin of these issues and provide you with some suggestions for successfully handling them.
![Atmega8 Usb To Serial Converter Atmega8 Usb To Serial Converter](/uploads/1/2/6/4/126461624/561012845.jpg)
USB to Serial Converter using ATmega8 /48. Firmware included. The later PC or Notebook nowdays discontinued Serial Port (com) but many old peripheral still using one (serial port). Example if we downloaded firmware for AT89C51 usually using serial port. Really cheap USB to TTL on Atmega: 1.70$ Posted. Now, serial port have been replaced with USB on most computers. A common way to fix this issue is to use a USB to TTL converter or a USB to RS232 converter + MAX232. How can I use this with an AVR Atmega (I used a Atmega8 but any will do the trick). Serial connection on a micro is TTL.
The Evolution from RS-232 to USB
In the old days of personal computers, one of the primary connections available was the RS-232 serial port. Apart from the parallel port, it was the primary means to connect an external device. The connector was reduced from a 25-pin connector to a 9-pin connector, but RS-232 ports remained present on every computer for many years. Built-in RS-232 ports featured direct mapping to memory and worked at a high priority. Data practically flowed directly to and from the software that was accessing the serial port.
In 1996, the Universal Serial Bus (USB) standard was introduced as a replacement for the serial connector and other connector types that were typically found on the back of computers. The USB provided smaller connectors and more data throughput than the serial and parallel interfaces it replaced.
USB devices have high throughput, but they use a shared data bus. Data is wrapped up and transferred in packets. To handle the packets and move data in and out of the program accessing the USB device, a software driver is needed. The software driver sits between the hardware and the computer program you are using, and it must be installed and working correctly.
The Necessity of an Adapter
With the widespread adoption of USB, most computers sold now do not have an RS-232 port. Therefore, to connect an RS-232 device (such as a CR1000) to a computer, you need to use a USB to RS-232 adapter, such as the 17394 converter.
While USB to RS-232 adapters perform a necessary function, they do have some limitations. For example, there are three types of problems that you may encounter when using a USB to RS-232 adapter:
- Driver issues
- Hardware issues
- Performance issues
Issue #1: Driver
The most common problem that our customers encounter with a USB to RS-232 adapter is getting the proper driver installed. The driver must correspond to the chip inside the cable—not to the manufacturer of the cable.
For USB to RS-232 chips, there are two primary manufacturers: Prolific and FTDI. Because off-brand chips with poor drivers are unreliable, Campbell Scientific recommends and currently sells a cable using an FTDI chip (part number 17394). We chose this cable because it uses a chip that has a certified driver available on Windows Update. (The older cables were silver in color and did not have a driver available for Windows beyond version 7.)
Tip: Test your USB adapters in the office with your field computer. When you are in the field, your computer won’t have an Internet connection to automatically download and install the driver.
If the driver for your adapter is not automatically installed or cannot be installed from a CD, you will need to identify the chip in your cable and locate the driver on the Internet. Some manufacturers identify on their packaging which chip is used inside their cable. You can also identify a cable’s chip from the Windows Device Manager by following these steps:
- In the Windows Device Manager, right-click your device from the list.
- In the drop-down menu that opens, select Properties.
- In the Properties dialog box, select the Details tab.
- In the Property field, select Hardware Ids from the drop-down menu.
- In the Value field, there is both a VID (Vendor ID) and a PID (Product ID). These IDs respectively indicate the manufacturer and the model number of the chip.
- In the example above, I did a quick Internet search for VID 0403 PID 6011, which revealed to me that the chip is an FT4232 manufactured by FTDI.
- After you know your chip type and manufacturer, you can locate and download the correct driver for your version of Windows.
Issue #2: Hardware
USB to RS-232 adapters are commodity pieces of computer equipment. As much as we all wish that everything was as reliable as the CR1000, all adapter cables eventually fail.
Although there are two primary companies that manufacture USB to RS-232 adapter chips, there are many cable manufacturers who offer varying levels of cable quality.
- Higher-quality, industrial models should last longer, but they wear out over time—just like any field tool.
- A poorly constructed cable could have components that fail in a short period of time—perhaps even by the time you receive the cable.
I have seen several cases where old cables could no longer handle 115200 baud, but the cables still worked on low baud rates. There have been many more cases where a USB cable stopped working half-way through a day in the field.
Tip: If your field site is far from your office, take two USB to RS-232 cables with you. Lost time in the field can be a lot more costly than the purchase price of a second cable.
Issue #3: Performance
As mentioned previously, USB uses a shared data bus with packetized communication. The packetized communication introduced some latency (data transfer time) that wasn’t present with built-in RS-232 ports. Unfortunately, latency makes a noticeable difference when you download large amounts of data or upload a new operating system.
The driver for FTDI chips allows you to lower the latency time on packets. To do this, you can use the Latency Timer field, which is accessed through the Windows Device Manager. Follow these steps:
- From the Windows Device Manager, right-click your device from the list.
- In the drop-down menu that opens, select Properties.
- Click the Port Settings tab.
- Click the Advanced… button.
- In the Advanced Settings window, navigate to the Latency Timer field, and reduce the setting to 1 for best performance.
In addition to lowering your latency time, I also recommend disabling the Selective Suspend option for your cable. The Selective Suspend option allows Windows to put your hardware to sleep, which can result in corrupt data packets. To disable the Selective Suspend option, clear the checkbox for the Enable Selective Suspend field on the Advanced Settings window for your device.
Note: The Selective Suspend option is already disabled by default in the FTDI driver.
Conclusion
Newer data logger designs, such as the CR6, feature a native USB connection. Many devices, however, will feature RS-232 connections for years to come, and we’ll need to continue using USB to RS-232 adapter cables. I hope the suggestions I’ve provided help. Feel free to share any USB to RS-232 issues that you have encountered by posting a comment below.
Here you will find useful tools, utilities and diagnostics software for serial communication, including drivers and user manuals for all our products. |
Recommended reading: |
5 Steps for Selecting the Right USB to Serial adapter |
Free Useful Tools and Diagnostics Software for Serial Communication | |||
AccessPort 1.37 | COM port terminal software for Windows | AccessPort137.zip | 441KB |
Tera Term | Terminal software alternative 1 for Windows | TeraTerm.zip | 7.32MB |
Putty | Terminal software alternative 2 for Windows | Putty.zip | 444KB |
US-TCP232-Test | Serial Ethernet/wlan test utility (WF500B, WF485, US2000B) | serial-ethernet-wlan-test-utility.zip | 460KB |
USR-WIFI232-6xx,A2,B2,D2 | Config utility for Ethernet/wlan converters (WF500B, WF485, US2000B) | config-utility-for-usr-converters.zip | 2.82MB |
ZTerm | Terminal software for MAC | ZTerm.zip | 678KB |
RS232 Data Logger | RS232 Data Logger | RS232 Data Logger.zip | 780KB |
Portmon | Monitor Serial and parallel ports | Portmon.zip | 190KB |
Hercules | Advanced Multi port (TCP, COM) terminal software | HerculesSetup.zip | 567KB |
Mitty | (Multi-Threaded TTY) is an easy to use high performance RS-232 serial terminal program. | Mitty.zip | 21.9KB |
YAT | Yat (Yet Another Terminal), Serial COM terminal program | YAT.zip | 1.04MB |
Serial COM Player | This software records and plays back serial data from your computer's serial ports | Serial Player.zip | 160KB |
ezTerm | TCP terminal software | Ezterm.zip | 67.50KB |
Serial Null | Simulates RS232 serial ports connected via virtual null-modem | SerialNull.zip | 563KB |
Serial Remap | Remaps all data from one serial port to another | SerialRemap.zip | 375KB |
Serial Trace | Monitors, displays, logs and analyzes all serial port activity | SerialTrace.zip | 566KB |
SAL232 | Serial port analyzer and logger | Sal232.zip | 262KB |
COM Port Stress Test | Generates a serial stream of data with random comm. settings | Comstresstest.zip | 3.34MB |
COM Port Data Emulator | Emulates a COM port or an Ethernet device, that generates a serial stream of data. The program can create a data flow, wrap it to data packets (RS232, TCP/IP or UDP) and send to a port | ComEmulator.zip | 3.43MB |
RealTerm | Advanced Serial terminal capturing, controlling and debugging | RealTerm.zip | 860KB |
Acrylic WiFi | The Most Advanced WLAN Scanner | Acrylic_WiFi_scanner.zip | 4.21MB |
RemSerial | Virtual COM software for Linux (tested with BF430 and XS1000) | remserial.zip | 9.13KB |
Below are drivers and datasheets for most of our products
Serial RS232, RS485 and RS422 | ||||
Part no. | Description | Processor | Files | Size |
XS202 | RS232 to RS422 port-powered | MAX491 / Philips HEF4093 | Datasheet.pdf | 155KB |
XS201A | RS232 to RS485 port-powered | MAX485E / Philips74HCT14 | Datasheet.pdf | 127KB |
XS203 | RS232 to RS485/422 port-powered | Datasheet.pdf | 134KB | |
XS216 | RS232 to RS485/422 Industrial | Datasheet.pdf | 145KB | |
XS503 | RS232 to RS485 / RS422 Ext Pwr, Iso | Datasheet.pdf | 130KB | |
AN232ISO | RS232 Optical Isolator 3-wire | TLP521 / ICL7660 | Datasheet.pdf | 124KB |
XS2112 | RS232 Optical Isolator 8-wire | Datasheet.pdf | 135KB | |
XS202 | RS232 Repeater | MAX491 / Philips HEF4093 | Datasheet.pdf | 155KB |
![Atmega328p Atmega328p](http://1.bp.blogspot.com/-mJaqGnAZEzw/UX4doWBWIGI/AAAAAAAAAgY/BgvtFmPO0n4/w1200-h630-p-k-no-nu/schematic-usb-to-serial-converter.gif)
USB to Serial RS232 | ||||
Part no. | Description | Processor | Files | Size |
ANU232Mi | USB to RS232 Mini | Prolific PL2303 | Drivers / Datasheets.zip | 4.16MB |
XS882 | USB to RS232 - Mini PRO | FTDI FT232BL | Drivers / Datasheets.zip | 4.16MB |
ANU232STD | USB to RS232 Standard | Prolific PL2303 | Drivers / Datasheets.zip | 4.16MB |
XS8801 | USB to RS232 Professional | FTDI FT232BL | Drivers / Datasheets.zip | 11.0MB |
XS880 | USB to RS232 Ultimate | FTDI FT232BL | Drivers / Datasheets.zip | 11.0MB |
Y-106 | USB to 2 x RS232 | MosChip MCS7820 | Drivers / Datasheets.zip | 8.48MB |
UMC-104 | USB to 4 x RS232 | FTDI FT232BL | Drivers / Datasheets.zip | 11.0MB |
USB to Serial RS485 and RS422 | ||||
Part no. | Description | Processor | Files | Size |
US485MIO | USB to RS485 Mini | SilLabs CP2102 | Drivers / Datasheets.zip | 11.5MB |
MWE820A | USB to RS485/422 Mini | SilLabs CP2102 | Drivers / Datasheets.zip | 11.5MB |
XS885 | USB to RS485/422 Mini Indust. | FTDI FT232RL | Drivers / Datasheets.zip | 11.0MB |
XS850 | USB to RS485 / RS422 Standard | Prolific PL2303 | Drivers / Datasheets.zip | 4.16MB |
XS890 | USB to RS485/422 Professional | FTDI FT232BL | Drivers / Datasheets.zip | 11.0MB |
SN-060519 | USB to RS485 Compact Pro | FTDI FT232BL | Drivers / Datasheets.zip | 11.0MB |
U485G | USB to RS422/485 Isolated | FTDI FT232BL | Drivers / Datasheets.zip | 11.0MB |
MWE820B | USB to RS232/485/422 Isolated | SilLabs CP2102 | Drivers / Datasheets.zip | 11.5MB |
Wireless Serial | ||||
Part no. | Description | Processor | Files | Size |
WA-232B | Serial WiFi Adapter | Broadcom BCM4390 | Utilities + Manuals.zip | 7.52MB |
YSC10U | RS232 Wireless RF 1600 FT | SP232 / LPC922F / CC1101 | Drivers + User Manual.zip | 1.46MB |
YSC30L | RS232/485 Wireless RF 9800 FT | SP232 / LPC921F / CC1101 | Drivers + User Manual.zip | 1.24MB |
UCBT232B | Bluetooth to Serial Adapter | CSR BC04 | User manual + Tera Term.zip | 8.56MB |
UCBT232EXA | Bluetooth to Serial Adapter, Industrial | CSR BC04 | User manual + Tera Term.zip | 8.56MB |
BL34 | External Bluetooth Dongle 100ft | Conwise CW6626 | Drivers Win 98, 2000, XP.zip | 157KB |
ES-388 | External Bluetooth Dongle 300ft | Drivers XP, Vista (32/64-bit).zip | 1.09MB | |
Bluesoleil v.2.3 | Bluetooth admin software. 98/2000/XP/2003, 32-bit. Full | Bluesoleil 2.3.zip | 27MB | |
Toshiba BT Stack | Bluetooth admin software. XP, Vista, 7, 8, 32/64-bit. 30 day Trial | Toshiba BT Stack v91001.zip | 77.9MB |
Serial over Ethernet | ||||
Part no. | Description | Processor | Files | Size |
XS1000 | 1 x Serial to Ethernet Server STD | IC+ IP210T | VCOM + Datasheet, all OS.zip | 18.94MB |
BF430 | 1 x Serial to Ethernet Server PRO | RDC R1610-G | Toolbox.zip | 13.7MB |
HL-SE02P-V1 | 2 x Serial to Ethernet Server Dual | ARM7 | VCOM + User Manual | 5.13KB |
PCI and PC Cards | ||||
Part no. | Description | Processor | Files | Size |
ANPCI232X2 | PCI Serial Card 2 x port | Moschip MSC9865 | Drivers / Datasheets.zip | 3.28MB |
PCIEX2P | PCI Express Serial 2 x port | Moschip MCS9922 | Drivers / Datasheets.zip | 4.78MB |
ANEXPSS1P | Serial ExpressCard 1 x port | Prolific PL2303 | Drivers / Datasheets.zip | 4.16MB |
ANPCM232 | PCMCIA Serial 1 x port | Oxford OXCB950 | Drivers / Datasheets.zip | 1.14MB |