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ATSAM4S-XPLD
1075
SAM4S [DATASHEET]
11100E–ATARM–24-Jul-13
Figure 43-17.SPI Slave Mode with (CPOL = NCPHA = 0) or (CPOL = NCPHA = 1)
43.11.3.1Maximum SPI Frequency
The following formulas give maximum SPI frequency in master read and write modes and in slave read and write modes.
Master Write Mode
The SPI is only sending data to a slave device such as an LCD, for example. The limit is given by SPI
2
(or SPI
5
)
timing. Since it gives a maximum frequency above the maximum pad speed (see
), the max SPI frequency is the one from the pad.
Master Read Mode
T
valid
is the slave time response to output data after detecting an SPCK edge. For Atmel SPI DataFlash
(AT45DB642D), T
valid
(or T
v
) is 12 ns Max.
In the formula above, F
SPCK
Max = 33.0 MHz @ VDDIO = 3.3V.
Slave Read Mode
In slave mode, SPCK is the input clock for the SPI. The max SPCK frequency is given by setup and hold timings
SPI
SPI
7
/SPI
8
(or SPI
10
/SPI
11
). Since this gives a frequency well above the pad limit, the limit in slave read mode is
given by SPCK pad.
Slave Write Mode
For 3.3V I/O domain and SPI6, F
SPCK
Max = 25 MHz. T
setup
is the setup time from the master before sampling data.
SPCK
MISO
MOSI
SPI
9
SPI
10
SPI
11
NPCS0
SPI
14
SPI
15
f
SPCK
Max
1
SP I
0
orSPI
3
(
) T
valid
+
----------------------------------------------------------
=
f
SPCK
Max
1
2
x S
( PI
6
max
orSPI
9
max
(
) T
setup
)
+
------------------------------------------------------------------------------------------
=