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SWRU294
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7 Connecting an external MCU to SmartRF TrxEB
You can easily connect an external MCU to a SmartRF TrxEB and use it to control the EM board
mounted on the TrxEB. This chapter gives a quick overview over the signals that must be
connected to enable your external MCU to control the EM.
7.1 Disable SmartRF TrxEB MCUs
To avoid any signal conflicts between the MCUs onboard the SmartRF TrxEB (MSP430 and USB
MCU) and the external MCU, both onboard MCUs should be disabled.
Disable the USB MCU by setting mode selection switch S2 to “Disable” position (Figure 18a).
To hold the onboard MSP430 MCU in reset state, short circuit pins 1-2 on header P4 as shown in
Figure 18b. An alternative, more power efficient option is to program the onboard MSP430 with
you own, custom software which configures the MSP430 pins to minimize current consumption
and makes the MSP430 enter a low-power mode [5].
a) Disable USB MCU b) Hold MSP430 in reset
Figure 18
– Switch and jumper settings to disable both SmartRF TrxEB MCUs
7.2 Select power source
When connecting an external MCU board to the SmartRF TrxEB, there are typically two options
for powering the boards, both consisting of sharing a power source. The first is to let the external
MCU board draw power from the SmartRF TrxEB; the second is to power the SmartRF TrxEB
from an external power source. It is in both cases important that the voltage levels on shared
signals are the same.
7.2.1 Power external MCU from SmartRF TrxEB
Power the external MCU board by connecting it to IO_PWR (P9) and GND (P6) on SmartRF
TrxEB, shown in Figure 19.
Figure 19
– Power external MCU board by connecting it to IO_PWR and GND