Instructions

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On the F5529 LaunchPad, the backchannel UART is implemented with the USCI_A1 module. The RTS

and CTS flow control signals are implemented on the P6.7 and P1.7 I/O pins, respectively. All of these

locations are hardwired on the F5529 LaunchPad and are independent from the 40-pin BoosterPack

header.

Table 7 shows some constants in bcUart.h that define the library's behavior.

Table 7. Backchannel Library: Constants to Configure

Constant Description

UCA1_OS

UCA1_BR0

Set the baudrate. Must be adjusted if SMCLK speed or baudrate are configured to anything

UCA1_BR1

other than 8 MHz and 28.8 kbps, respectively. See bcUart.h for instructions.

UCA1_BRS

UCA1_BRF

BC_USE_HW_FLOW_CONTROL If hardware flow control is desired, un-comment this #define

BC_RXBUF_SIZE Set the size of the buffer that receives data over the backchannel UART.

When this number of bytes have been received into the receive buffer, the

BC_RX_WAKE_THRESH bcUartRxThresholdReached flag is set to TRUE, and the main application is awakened from

any LPM it might be in.

Table 8 shows the library's function calls.

Table 8. Backchannel Library: Functions

Function Description

void bcUartInit(void) Call once during program initialization

void bcUartSend(uint8_t * buf, uint8_t len) Send len bytes stored at buf over the UART.

Copy any bytes received into the library's UART receive buffer into buf

uint16_t bcUartReceiveBytesInBuffer(uint8_t* buf)

and return the number of bytes copied.

The library includes a definition of the USCI_A1 ISR, which copies

USCI_A1 Interrupt Vector

incoming UART bytes into a receive buffer.

If the application uses the USCI_A1 ISR for another purpose in addition to the backchannel, it is

necessary to merge that operation with the backchannel library's ISR.

3.6.5 Code Description: Initialization

First, the device must be initialized. Although called from main(), much of this initialization is defined within

hal.c and hal.h. Most of the examples in the USB API v4.0 and later include this hardware abstraction

layer (HAL) file to assist in running on multiple USB-equipped boards available from TI. Clocks, power,

and port settings can be hardware-specific and, thus, are handled by the HAL. This demo follows that

convention.

3.6.5.1 Stopping the Watchdog

The MSP430 contains a watchdog timer that is enabled by default. After a reset, an MSP430 application

has approximately 32 ms to either reconfigure the watchdog or put it on hold. Otherwise, the watchdog

resets the MSP430 device.

Watchdogs are an important part of writing robust production-level code, but if you are only experimenting

with the MCU, it is not helpful and can be obstructive. For this reason, the first line of code on many bench

applications is to simply disable the watchdog by setting the WDTHOLD bit.

3.6.5.2 Configuring V

CORE

Next, main() sets the PMMCOREV register field to 2. PMMCOREV controls the V

CORE

voltage, which is the

voltage at which the MCU's core circuitry operates. V

CORE

is generated from a low-dropout (LDO) regulator

inside the MCU's Power Management Module (PMM). Higher CPU operating speeds require higher V

CORE

levels, and higher V

CORE

levels result in higher quiescent current on the LDO. For this reason, V

CORE

programmable.

MSP430F5529 LaunchPad™ Development Tool (MSP

‑

EXP430F5529LP) SLAU533A–September 2013–Revised January 2014

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