User Manual

MG21USB Dongle Guide
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1.5 MG21 Bootloader mode and Reset control
Instead of having the BOOTLOAD and RESET push buttons on board, the USB Dongle HW design (shown below) makes use
of CP2102N’s modem control pins, i.e. DTS and RTS, for MG21 Reset control and entering the Bootloader mode.
Figure 1.3. USB Dongle host DTR for Reset and RTS for Bootloader Control
This achieves fail-safe application firmware update for the MG21 USB Dongle by the host application even when the original
NCP application firmware is corrupted somehow.
Note that the host RTS control pin (EFR_CTS) is used for both Bootloader control and HW flow control purposes. HW flow
control can still work in parallel and MG21 won’t false-enter Bootloader mode without the host DTR control triggers the Reset.
1.6 LED Indicators
Two LED indicators are provided for USB Dongle firmware application use:
 LD1 (GREEN) : PD03 (FEM_RXA)
 LD2 (RED) : PD02 (FEM_TXA)
1.7 PTA Debug Interface
The USB Dongle HW design has reserved the PTA Coexistence pins (REQUEST, PRIORITY, GRANT) and the RF debug
FEM_TXA, FEM_RXA debug pins exposed to PTA debug test points, i.e. T9 to T14. Please refer to session 1.10 for the PTA
test points description.
To enable PTA, a Zigbee NCP or an OpenThread RCP sample project needs to install the Coexistence plugin and configure
the PTA pins accordingly. FEM_TXA, FEM_RX are recommended to be enabled to helps the PTA debugging.