Nordic nRF5340 User Guide

Interface MCU
GPIO nRF5340 nRF5340 UART
P0.19 RTS
P0.20 TXD
P0.21 CTS
P0.22 RXD
Table 1: Relationship of UART connections on nRF5340 and interface MCU
The UART signals are routed directly to the interface MCU. The UART pins connected to the interface MCU
are tri-stated when no terminal is connected to the virtual COM port on the computer.
Note: The terminal software used must send a Data Terminal Ready (DTR) signal to configure the
UART interface MCU pins.
The P0.19 (Request to Send (RTS)) and P0.21 (Clear to Send (CTS)) can be used freely when HWFC is
disabled on the SoC.
4.2.1 Dynamic HWFC handling
When the interface MCU receives a DTR signal from a terminal, it performs automatic HWFC detection.
Automatic HWFC detection is done by driving P0.21 (CTS) from the interface MCU and evaluating the state
of P0.19 (RTS) when the first data is sent or received. If the state of P0.19 (RTS) is high, HWFC is assumed
not to be used. If HWFC is not detected, both CTS and RTS can be used freely by the nRF application.
After a power-on reset of the interface MCU, all UART lines are tri-stated when no terminal is connected
to the virtual COM port. Due to the dynamic HWFC handling, if HWFC has been used and detected, P0.21
(CTS) will be driven by the interface MCU until a power-on reset has been performed or until a new DTR
signal is received and the detection is redone.
To ensure that the UART lines are not affected by the interface MCU, the solder bridges for these signals
can be cut and later resoldered if needed. This might be necessary if UART without HWFC is needed while
P0.19 (RTS) and P0.21 (CTS) are used for other purposes.
4.3 MSD
The interface MCU features an Mass Storage Device (MSD). This makes the development kit appear as an
external drive on your computer.
This drive can be used for drag-and-drop programming. However, files cannot be stored on this drive. By
copying a HEX file to the drive, the interface MCU will program the file to the device.
Note:
• Windows might try to defragment the MSD part of the interface MCU. If this happens, the
interface MCU will disconnect and be unresponsive. To return to normal operation, the
development kit must be power cycled.
• Your antivirus software might try to scan the MSD part of the interface MCU. Some antivirus
programs trigger a false positive alert in one of the files and quarantine the unit. If this happens,
the interface MCU will become unresponsive.
• If the computer is set up to boot from USB, it can try to boot from the development kit if the
development kit is connected during boot. This can be avoided by unplugging the development
kit before a computer restart, or changing the boot sequence of the computer.
4406_489 v1.0
10

Nordic nRF5340 Specifications

General

Brand	Nordic
Model	nRF5340
Category	Computer Hardware
Language	English