USART Operation: SPI Mode
18-5
USART Peripheral Interface, SPI Mode
18.2.2 Master Mode
Figure 18−2. USART Master and External Slave
Receive Buffer UxRXBUF
Receive Shift Register
MSB
LSB
Transmit Buffer UxTXBUF
Transmit Shift Register
MSB
LSB
SPI Receive Buffer
Data Shift Register (DSR)
MSB
LSB
SOMI
SOMI
SIMO
SIMO
MASTER
SLAVE
Px.x
STE
STE
SS
Port.x
UCLK
SCLK
MSP430 USART
COMMON SPI
Figure 18−2 shows the USART as a master in both 3-pin and 4-pin
configurations. The USART initiates a data transfer when data is moved to the
transmit data buffer UxTXBUF. The UxTXBUF data is moved to the TX shift
register when the TX shift register is empty, initiating data transfer on SIMO
starting with the most-significant bit. Data on SOMI is shifted into the receive
shift register on the opposite clock edge, starting with the most-significant bit.
When the character is received, the receive data is moved from the RX shift
register to the received data buffer UxRXBUF and the receive interrupt flag,
URXIFGx, is set, indicating the RX/TX operation is complete.
A set transmit interrupt flag, UTXIFGx, indicates that data has moved from
UxTXBUF to the TX shift register and UxTXBUF is ready for new data. It does
not indicate RX/TX completion. In master mode, the completion of an active
transmission is indicated by a set transmitter empty bit TXEPT = 1.
To receive data into the USART in master mode, data must be written to
UxTXBUF because receive and transmit operations operate concurrently.
Four-Pin SPI Master Mode
In 4-pin master mode, STE is used to prevent conflicts with another master.
The master operates normally when STE is high. When STE is low:
-
SIMO and UCLK are set to inputs and no longer drive the bus
-
The error bit FE is set indicating a communication integrity violation to be
handled by the user
A low STE signal does not reset the USART module. The STE input signal is
not used in 3-pin master mode.
Summary of Contents for MSP430x4xx Family
Page 1: ...MSP430x4xx Family 2007 Mixed Signal Products User s Guide SLAU056G ...
Page 2: ......
Page 6: ...vi ...
Page 114: ...3 76 RISC 16 Bit CPU ...
Page 304: ...5 20 FLL Clock Module ...
Page 340: ...7 8 Supply Voltage Supervisor ...
Page 348: ...8 8 16 Bit Hardware Multiplier ...
Page 372: ...9 24 32 Bit Hardware Multiplier ...
Page 400: ...10 28 DMA Controller ...
Page 428: ...13 10 Basic Timer1 ...
Page 466: ...15 24 Timer_A ...
Page 522: ...17 30 USART Peripheral Interface UART Mode ...
Page 544: ...18 22 USART Peripheral Interface SPI Mode ...
Page 672: ...23 12 Comparator_A ...
Page 692: ...24 20 LCD Controller ...
Page 746: ...26 28 ADC12 ...