Isolated RS232 and RS485 Expansion
Board User Guide
The Silicon Labs Isolated RS232 and RS485 Evaluation Board is
a hardware plugin card for EFM8 and EFM32 Starter Kits (STKs).
The Isolated RS232 and RS485 EXP is intended to help demon-
strate and evaluate applications for Silicon Labs isolation and
MCU products. Silicon Labs isolation products create a CMOS
barrier to protect components while still allowing for communica-
tion and power transfer. Silicon Labs MCU products offer broad
solutions for low power, industrial, consumer electronics and
more. Software demos are available for connecting the MCU Iso-
lated RS232 and RS485 EXP and can be downloaded and run
through Simplicity Studio™. The demos send signals across the
isolation barrier and the message is seen by the user on a termi-
nal or on the screen of the MCU STK. They also showcase Silicon
Labs ISOVolt technology as the MCU powers components across
the isolation barrier.
Note:
For full use and evaluation of the Isolated RS232 and RS485 EXP a MCU STK is
needed. For full demonstration, two MCU STKs and two Isolated RS232 and RS485
EXPs are needed to communicate between one another. Software examples are provi-
ded for two MCU STKs, the EFM32 Wonder Gecko Starter Kit EFM32WG-STK3800 and
the EFM8 Universal Bee 1 Starter Kit SLSTK2000A.
KEY FEATURES OR KEY POINTS
• 20-pin headers for connection to EFM8
and EFM32 starter kits
• Software demos available in Simplicity
Studio
• Power and communication over isolation
barrier
• Jumpers for easy manual control of input
signals
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Isolated RS232 and RS485 Expansion Board User Guide
Kit Contents
1. Kit Contents
The Isolated RS232 and RS485 Evaluation Kit contains the Expansion Board, null modem DB9 cable, and a QR code card for quick
access to information. Other features of the kit include the following items:
• 20-pin header to connect to the MCU STK
• DB9 port for RS232
• Screw terminals for RS485
• Power of the EXP board through the 20-pin header or screw terminals
• Breakout points for precise evaluation of specific systems
• Isolation barrier to separate the STK MCU from the EXP
• Easy use through Simplicity Studio
Figure 1.1. Annotated Isolated RS232 and RS485 EXP
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Isolated RS232 and RS485 Expansion Board User Guide
Details and Applications
2. Details and Applications
This evaluation kit and associated demos allow the MCU STK, Isolated RS232 and RS485 EXP, and sensors to communicate through
the RS ports on the EXP board while being isolated. The MCU communicates through UART to the isolation devices. These signals are
carried through the barrier into an RS transceiver which converts it to either RS485 or RS232. Then, the RS ports can be read by a host
or another MCU/EXP combination. The RS communication protocols, especially RS485, are widely used in industrial and commercial
applications where long wires, multiple nodes, high power, or noise are common. Isolation is widely needed in the following markets:
• Industrial automation systems
• Medical electronics
• Hybrid electric vehicles
• PLCs, distributed control systems
• Isolated switch mode supplies
• Isolated ADC and DACs
• Motor control
• Power inverters
• Communication systems
All of these market segments use various communication protocols, such as RS485, CAN, I2C, SPI, UART and the combination of Sili-
con Labs isolators and MCU products can serve any of these segments.
2.1 Hardware
The Isolated RS232 and RS485 EXP key components are:
• Si88242ED-IS - Digital Isolator with Integrated DC-DC Converter containing 4 unidirectional channels, Automotive, 20-pin SOIC
• Si8631BB-B-IS1- Digital CMOS Isolator with 3 channels, up to 150Mbps, Automotive, 16-Pin SOIC
• ISL3332IAZ – RS232 and RS485 transceiver
• UTB02268s – Power inverter
The flow of the EXP board connected to an MCU Starter Kit is shown in the figure below.
UART
UART
MCU
Isolator
RS
Transciever
RS242
OR
RS485
DB9 or RS485
port
Figure 2.1. Isolated RS232 and RS485 EXP and MCU STK block diagram
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Isolated RS232 and RS485 Expansion Board User Guide
Details and Applications
2.1.1 Jumpers and Headers
Isolated RS232 and RS485 EXP contains many jumpers and headers for easy debugging and added functionality.
J1 and J2 contain the 4 wire RS232 signals with J1 coming from the MCU and J2 coming from the transceiver.
J1 also contains the shutdown jumper for the isolator. With this populated, the DC-DC converter is disabled and no power will be sent
over the barrier. The other side of the isolation barrier must then be powered separately via the J5 port. With J1 unpopulated, power will
flow over the isolation barrier and only one power source is needed.
J3 and J4 contain the RS485 signals with J3 coming from the MCU and J4 coming from the transceiver.
JP1 and JP2 allow loopback of the RS232 signals in the occurrence that no RS232 host or device is available.
JP4 and JP5 allow for RS485 biasing.
The schematics for the board are found in Figure 3.
Figure 2.2. Isolated USB EXP Schematic
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Isolated RS232 and RS485 Expansion Board User Guide
Details and Applications
2.1.2 Header Connections
The Isolated RS232 and RS485 EXP connects to the MCU STK via a 20-pin header. On the EXP board is the receptacle and the MCU
STK has the pins. They align in such a way to take advantage of certain MCU peripherals, such as UART and GPIOs. See the figure
below for the exact pin out. See the individual MCU STK user guides for each specific board. The one shown below is the EFM32
Wonder Gecko Starter Kit pin out.
Figure 2.3. EFM32 WG STK 20-pin header (left) and the Isolated RS232 and RS485 EXP receptacle header (right)
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