[Technology Report]
Connect The Dots Toward Efficient Serial-To-Ethernet Adapter Design
The RS-232 serial-to-Ethernet adapter cost-effectively bridges legacy systems to the latest networking applications.
Back in the 1970s and 1980s, when the RS-232 serial protocol was being adapted to the address the demands of electronic terminals and personal computers, few could have imagined that it would become such a standard feature. Thousands of industrial devices were developed based on the RS-232 interface. But for electronic communications, the evolutionary process was already kicking into a higher gear.
Today, Ethernet is a well-defined standard for local and wide-area networks. Countless devices access the Internet using TCP/IP over Ethernet. Despite the presence of other physical-layer implementations, Ethernet is here to stay for many years until, of course, electronic communications evolves into something else and faster, more advanced protocols are required.
Myriad new designs continue to use Ethernet as the primary network standard. Others may implement different physical interfaces but still use TCP/IP to access networks, such as the Internet. In fact, the wide acceptance of TCP/IP over Ethernet is a primary reason behind the Internet’s rapid expansion over the last couple of decades. But what happened to RS-232?
SUSTAINABLE EVOLUTION Millions of electronic products still use RS-232 as a serial interface. This is particularly true in developing countries, where developers may lack the budgets to leapfrog from legacy systems to new technology. Therefore, some form of sustainable evolution must be considered.
A cost-effective way to operate in this new environment is the RS-232 serial-to-Ethernet adapter, the “missing link” in the evolutionary chain that brings legacy systems into a whole new panorama of networking applications. When evaluating a serialto- Ethernet bridge, developers should consider:
• Small size: An optimized printed-circuit-board (PCB) design, with fewer highly integrated components, reduces the project’s footprint and its cost.
• Operating voltage: This should be compatible with common serial communications standards, such as RS-232 and RS-485.
• Adaptability: Customizable and layered software along with flexible hardware designs are highly recommended to make the bridge more adaptable to different applications.
• Usability: Simple interfaces for configuration and monitoring, such as GUIs and LED indicators, improve ease of use.
• Performance: The bridge should be able to convert RS-232 and/ or RS-485 to Ethernet without any user inconveniences. Using a microcontroller with a serial communications interface and an Ethernet media access controller (MAC) is recommended. The device should have just enough performance for the required application to keep costs down.
• System cost: Developers should strive to keep system costs as low as possible.
COST-EFFECTIVE, PLEASE What is cost-effective when you are trying to link the old with the new? The software must be complementary, and hardware costs should be minimized. As such, a cost-free but still robust and customizable software approach is strongly recommended.
Ready-to-use operating systems and stacks can ease this task. Thus, it takes minimal effort to add, modify, or remove software modules compared to developing your own task scheduler, Ethernet TCP/IP stack, or application from scratch. Today, you can find a wide variety of royalty-free and open-source stacks and operating systems. Choose wisely, though, since they will be closely tied to hardware and community support.
You might have an amazing application that fulfills the serial-to- Ethernet bridge functionality. But if the chosen processing device (microprocessor or microcontroller) exceeds the performance requirements, the cost will be too high. If the performance is inadequate, then the functionality of the final product will fall short of application requirements.
Microprocessors can easily fulfill this task. However, microcontrollers have evolved to the point where they can run operating systems while providing Ethernet connectivity at a much lower price. A serial-to-Ethernet bridge can be implemented easily using a low-end 32-bit microcontroller with low SRAM and flash size.
MAKE DESIGN AND CUSTOMIZATION EASY Even when you have found the right costeffective microcontroller with the required performance and peripherals, along with enough SRAM and flash to run a reduced operating system and basic Ethernet stack, you still have to assemble all of these software and hardware blocks. Engineering time impacts system cost, so how do you simplify development?
A layered software architecture is recommended. All of the different blocks can be put together to create a software environment that will organize the development process. This can directly impact engineering time and later customization of serialto- Ethernet bridges.
Such a layered software model is based in splitting several main software blocks into layers and essentially making an abstraction of the hardware used. The hardware abstraction layer (HAL) is defined as the collection of software components that make direct access to the hardware resources, including peripherals, configuration registers, optimized assembler routines (with their appropriate prototypes), pre-compiled object code libraries, or any other hardware dependent resource, through the HAL/HW interface.
Hi folks, thanks for the feedback! if any of you is interested in full schematics, code and deeper explaination just send an email to b07293@freescale.com and I can send you the info.
best regards
Cuau
Cuauhtemoc -September 02, 2009
TECHNICALLY ... zero ohm resistors don't isolate; they CONNECT. But a good article all the same.
Anonymous -September 02, 2009
Interesting Ad for Freescale, but nothing special here. We implemented a complete Ethernet to Serial interface years ago with a cute little 8 bit processor by Ubicom. With the ethernet MAC and PHY on board with the CPU, 64K Flash and 20K RAM the entire entire design was quite simple and supported RFC2217+ on a complete TCP/IP stack. I'd be embarrassed to produce such an article.
Michael Klos -September 01, 2009
I guess I am an ID 10T. Please help me. Where do I find the reference design the Freescale folks mention ?
"Free- RTOS, LightweightIP (Ethernet-TCP/IP stack), and Freescale’s MCF51CN128 embedded controller have been used to create a specific reference design for a simple serial-to-Ethernet bridge."
How about some URLs that reference Free-RTOS , LightweightIP , etc.
Is an IDIOT asking for too much ?
Gus S. Calabrese -August 29, 2009
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