Texas Instruments MSP-EXP430FR5969, User Manual

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2.3.2 Application (or "Backchannel") UART
The backchannel UART allows communication with the USB host that isn't part of the target application's
main functionality. This is very useful during development, and also provides a communication channel to
the PC host side. This can be used to create GUIs and other programs on the PC that communicate with
the FR5969 LaunchPad.
The pathway of the backchannel UART is shown in Figure 10 . The backchannel UART (USCI_A0) is
independent of the UART on the 20-pin BoosterPack connector (USCI_A1).
On the host side, a virtual COM port for the application backchannel UART is generated when the
LaunchPad enumerates on the host. You can use any PC application that interfaces with COM ports,
including terminal applications like Hyperterminal or Docklight, to open this port and communicate with the
target application. You need to identify the COM port for the backchannel. On Windows PCs, Device
Manager can assist (see
Figure 6 ).
Figure 6. Application Backchannel UART in Device Manager
The backchannel UART is the "MSP Application UART1" port. In this case, Figure 6 shows COM13, but
this varies from one host PC to the next. After you identify the correct COM port, configure it in your host
application, according to its documentation. You can then open the port and begin talking to it from the
host.
On the target FR5969 side, the backchannel is connected to the USCI_A0 module.
The eZ-FET has a configurable baud rate, therefore, it is important that the PC application configures the
baud rate to be the same as the rate configured on the USCI_A0.
The eZ-FET also supports hardware flow control, if desired. Hardware flow control (CTS/RTS
handshaking) allows the target FR5969 and the emulator to tell each other to wait before sending more
data. At low baud rates and with simple target applications, flow control may not be necessary.
Applications with faster baud rates and more interrupts to service have a higher likelihood that they cannot
read the USCI_A0's RXBUF register in time, before the next byte arrives. If this happens, the USCI_A0's
UCA0STATW register will report an overrun error.
10 MSP430FR5969 LaunchPad™ Development Kit (MSP ‑ EXP430FR5969) SLAU535B – February 2014 – Revised July 2015
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