at91rm3400 ATMEL Corporation, at91rm3400 Datasheet - Page 238

• Manufacturer Part Number: at91rm3400
• Description: Atmel Advanced At91 Arm Microcontroller
• Manufacturer: ATMEL Corporation

Data Transfer
Figure 77. SPI Transfer Format (NCPHA = 1, 8 bits per transfer)
238
SPCK cycle (for reference)
NSS (to slave)
(from master)
(from slave)
(CPOL=0)
(CPOL=1)
AT91RM3400
Mode 1
Mode 3
SPCK
SPCK
MOSI
MISO
* Not defined, but normally MSB of previous character received.
Four modes are used for data transfers. These modes correspond to combinations of a pair of
parameters called clock polarity (CPOL) and clock phase (NCPHA) that determine the edges
of the clock signal on which the data are driven and sampled. Each of the two parameters has
two possible states, resulting in four possible combinations that are incompatible with one
another. Thus a master/slave pair must use the same parameter pair values to communicate.
If multiple slaves are used and fixed in different configurations, the master must reconfigure
itself each time it needs to communicate with a different slave.
Table 39 shows the four modes and corresponding parameter settings.
Table 39. SPI Bus Protocol Mode
Figure 77 and Figure 78 show examples of data transfers.
MSB
1
MSB
2
6
6
SPI Mode
0
1
2
3
3
5
5
4
4
4
5
3
3
6
6
CPOL
2
2
0
0
1
1
7
1
1
8
LSB
LSB
NCPHA
0
1
0
1
1790A–ATARM–11/03
*