Texas Instruments MSP430x1xx - Manual (Page 249)

13-3
USART Peripheral Interface, SPI Mode
13.2 USART Peripheral Interface, SPI Mode
The USART peripheral interface is a serial channel that shifts a serial bit
stream of 7 or 8 bits in and out of the MSP430. The SPI mode is chosen when
control bit SYNC in the USART control register (UCTL) is set.
13.2.1 SPI Mode Features
The features of the SPI mode are:
- Supports three-pin and four-pin SPI operations via SOMI, SIMO, UCLK,
and STE
- Master or slave mode
- Separate shift registers for receive (URXBUF) and transmit (UTXBUF)
- Double buffers for receiving and transmitting
- Has clock-polarity and clock-phase control
- Has clock-frequency control in master mode
- Supports a character length of seven or eight bits per character
Figure 13–2 shows the USART module in SPI mode.
Figure 13–2. Block Diagram of USART—SPI Mode
0
Receive Buffer URXBUF
SSEL0 SSEL1
ACLK
1
2
3
SMCLK
CKPH
Receive Shift Register
Receive Status
Baud-Rate Generator
Baud-Rate Register
Baud-Rate Generator
SYNC SYNC
SYNC
UCLKS
Transmit Shift Register
Transmit Buffer UTXBUF
0
1
1
0
1
0
Clock Phase and Polarity
SYNC CKPL
(UCLKI)
UCLKS
UCLK
SIMO
STE
SOMI
MM Listen
SYNC = 1
MSB First
MSB First
UCLKI
SMCLK