AT80SND1C-ROTIL datasheet(150/210 Pages) ATMEL

150 / 210 page

150

AT8xC51SND1C

4109E–8051–06/03

Figure 116. Data Transmission Format (CPHA = 1)

SS Management

Figure 115 shows an SPI transmission with CPHA = 0, where the first SCK edge is the

MSB capture point. Therefore the slave starts to output its MSB as soon as it is

selected: SS asserted to low level. SS must then be deasserted between each Byte

transmission (see Figure 117). SPDAT must be loaded with a data before SS is

asserted again.

Figure 116 shows an SPI transmission with CPHA = 1, where the first SCK edge is used

by the slave as a start of transmission signal. Therefore, SS may remain asserted

between each Byte transmission (see Figure 117).

Figure 117. SS Timing Diagram

Error Conditions

The following flags signal the SPI error conditions:

•

MODF in SPSTA signals a mode fault.

MODF flag is relevant only in master mode when SS usage is enabled (SSDIS bit

cleared). It signals when set that an other master on the bus has asserted SS pin

and so, may create a conflict on the bus with 2 master sending data at the same

time.

•

A mode fault automatically disables the SPI (SPEN cleared) and configures the SPI

in slave mode (MSTR cleared).

MODF flag can trigger an interrupt as explained in Section "Interrupt", page 151.

MODF flag is cleared by reading SPSTA and re-configuring SPI by writing to

SPCON.

•

WCOL in SPSTA signals a write collision.

WCOL flag is set when SPDAT is loaded while a transfer is on-going. In this case

data is not written to SPDAT and transfer continue uninterrupted. WCOL flag does

not trigger any interrupt and is relevant jointly with SPIF flag.

WCOL flag is cleared after reading SPSTA and writing new data to SPDAT while no

transfer is on-going.

MSB

bit 1

LSB

bit 2

bit 4

bit 3

bit 6

bit 5

bit 1

bit 2

bit 4

bit 3

bit 6

bit 5

MSB

LSB

MOSI (from master)

MISO (from slave)

SCK (CPOL = 1)

SCK (CPOL = 0)

SPEN (internal)

SCK cycle number

SS (to slave)

Capture point

SS (CPHA = 1)

SS (CPHA = 0)

SI/SO

Byte 1

Byte 2

Byte 3

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