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Daisy
Chaining MicroX Boards
MicroX Application Note
1 Introduction
Many of
the MicroX Main Boards (Single Board Computers) have 2 RJ45
connectors. If they are assembled with the RS485 interface option,
multiple boards can be daisy chained together as shown in Figure 1,
using standard RJ45 network cables.
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Figure 1
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All
boards shown in Figure 1 are connected to the same RS485 Data
and Power Bus, and can communicate with each other. In
addition, most of the MicroX boards have jumpers to connect pins 1
and 2 of the RJ45 connectors with the unregulated power on the board
(Input of the 2.1mm power jack). This means that only one boards
needs to be supplied with power (via it’s 2.1mm power jack),
and all other boards can obtain their power from the RS485 Data
and Power Bus.
2 RS485 Data and Power Bus
The RS485 line driver chip used on most of the
MicroX Boards is the MAX485 or equivalent chip. This chip is capable
of data rates up to 2.5Mbps, and can support up to 32 transmitters on
a single bus. The RS485 positive bus line is connected to pin 5 of
the RJ45 connector, and the negative bus line is connected to pin 4.
As mentioned previously, most of the MicroX boards
have jumpers to connect pins 1 and 2 of the RJ45 connectors with the
unregulated power on the board (Input of the 2.1mm power jack). Pins
3 and 6 are connected to ground. Figure 2 shows the typical
configuration.
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Figure 2
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Standard
RJ45 network cables (Not crossover cables) are used to connect
multiple boards together.
3 Supplying power to multiple boards
When using the power feature of the RS485
Data and Power Bus, it is VERY important that only one
board supplies the power (Has a DC transformer connected to it’s
2.1mm power jack), and all the rest source power from the bus. All
boards must have the jumper mounted that connects it’s
unregulated power to the RJ45 connector. The board with the DC
transformer will supply the power for all the other boards. See
Figure 1 for an example of multiple boards being supplied with power
from the RS485 Data and Power Bus – note that
only one board has a power cable connected to it’s 2.1mm power
jack!
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