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.
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