USART Operation: SPI Mode
18-6
USART Peripheral Interface, SPI Mode
18.2.3 Slave Mode
Figure 18−3. USART Slave and External Master
Receive Buffer UxRXBUF
Receive Shift Register
LSB
MSB
Transmit Buffer UxTXBUF
Transmit Shift Register
LSB
MSB
SPI Receive Buffer
Data Shift Register DSR
LSB
MSB
SOMI
SOMI
SIMO
SIMO
MASTER
SLAVE
Px.x
STE
STE
SS
Port.x
UCLK
SCLK
MSP430 USART
COMMON SPI
Figure 18−3 shows the USART as a slave in both 3-pin and 4-pin
configurations. UCLK is used as the input for the SPI clock and must be
supplied by the external master. The data-transfer rate is determined by this
clock and not by the internal baud rate generator. Data written to UxTXBUF
and moved to the TX shift register before the start of UCLK is transmitted on
SOMI. Data on SIMO is shifted into the receive shift register on the opposite
edge of UCLK and moved to UxRXBUF when the set number of bits are
received. When data is moved from the RX shift register to UxRXBUF, the
URXIFGx interrupt flag is set, indicating that data has been received. The
overrun error bit, OE, is set when the previously received data is not read from
UxRXBUF before new data is moved to UxRXBUF.
Four-Pin SPI Slave Mode
In 4-pin slave mode, STE is used by the slave to enable the transmit and
receive operations and is provided by the SPI master. When STE is low, the
slave operates normally. When STE is high:
-
Any receive operation in progress on SIMO is halted
-
SOMI is set to the input direction
A high STE signal does not reset the USART module. The STE input signal
is not used in 3-pin slave 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 ...