USCI Operation: SPI Mode
20-9
Universal Serial Communication Interface, SPI Mode
20.3.4 Slave Mode
Figure 20−3. USCI Slave and External Master
Receive Buffer
UCxRXBUF
Receive Shift Register
Transmit Buffer
UCxTXBUF
Transmit Shift Register
SPI Receive Buffer
Data Shift Register DSR
UCx
SOMI
SOMI
UCxSIMO
SIMO
MASTER
SLAVE
Px.x
UCxSTE
STE
SS
Port.x
UCxCLK
SCLK
MSP430 USCI
COMMON SPI
Figure 20−3 shows the USCI as a slave in both 3-pin and 4-pin configurations.
UCxCLK 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 bit clock generator. Data written to UCxTXBUF and moved to the
TX shift register before the start of UCxCLK is transmitted on UCxSOMI. Data
on UCxSIMO is shifted into the receive shift register on the opposite edge of
UCxCLK and moved to UCxRXBUF when the set number of bits are received.
When data is moved from the RX shift register to UCxRXBUF, the UCxRXIFG
interrupt flag is set, indicating that data has been received. The overrun error
bit, UCOE, is set when the previously received data is not read from
UCxRXBUF before new data is moved to UCxRXBUF.
Four-Pin SPI Slave Mode
In 4-pin slave mode, UCxSTE is used by the slave to enable the transmit and
receive operations and is provided by the SPI master. When UCxSTE is in the
slave-active state, the slave operates normally. When UCxSTE is in the
slave-inactive state:
-
Any receive operation in progress on UCxSIMO is halted
-
UCxSOMI is set to the input direction
-
The shift operation is halted until the UCxSTE line transitions into the slave
transmit active state.
The UCxSTE 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 ...