C8051F02X Datasheet, PDF (200/272 Pages) Silicon Laboratories – 8K ISP FLASH MCU Family

C8051F020/1/2/3
Multiple masters may reside on the same bus. A Mode Fault flag (MODF, SPI0CN.5) is set to logic 1 when SPI0 is
configured as a master (MSTEN = 1) and its slave select signal NSS is pulled low. When the Mode Fault flag is set,
the MSTEN and SPIEN bits of the SPI control register are cleared by hardware, thereby placing the SPI0 module in
an "off-line" state. In a multiple-master environment, the system controller should check the state of the SLVSEL flag
(SPI0CN.2) to ensure the bus is free before setting the MSTEN bit and initiating a data transfer.
19.3. Serial Clock Timing
As shown in Figure 19.4, four combinations of serial clock phase and polarity can be selected using the clock control
bits in the SPI0 Configuration Register (SPI0CFG). The CKPHA bit (SPI0CFG.7) selects one of two clock phases
(edge used to latch the data). The CKPOL bit (SPI0CFG.6) selects between an active-high or active-low clock. Both
master and slave devices must be configured to use the same clock phase and polarity. Note: SPI0 should be disabled
(by clearing the SPIEN bit, SPI0CN.0) while changing the clock phase and polarity.
The SPI0 Clock Rate Register (SPI0CKR) as shown in Figure 19.7 controls the master mode serial clock frequency.
This register is ignored when operating in slave mode.
Figure 19.4. Data/Clock Timing Diagram
SCK
(CKPOL=0, CKPHA=0)
SCK
(CKPOL=0, CKPHA=1)
SCK
(CKPOL=1, CKPHA=0)
SCK
(CKPOL=1, CKPHA=1)
MISO/MOSI
MSB
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
NSS
200
Rev. 1.4