Figure 33-5. Multiple Slaves in Parallel
MOSI
MISO
SCK
_SS
MOSI
MISO
SCK
_SS[0]
MOSI
MISO
SCK
_SS
_SS[n-1]
shift register
shift register
shift register
SPI Master
SPI Slave 0
SPI Slave n-1
Another configuration is multiple slaves in series, as in
. In this configuration, all
n attached slaves are connected in series. A common SS line is provided to all slaves, enabling them
simultaneously. The master must shift n characters for a complete transaction. Depending on the Master
Slave Select Enable bit (CTRLB.MSSEN), the SS line can be controlled either by hardware or user
software and normal GPIO.
Figure 33-6. Multiple Slaves in Series
MOSI
MISO
SCK
_SS
MOSI
MISO
SCK
_SS
MOSI
MISO
SCK
_SS
shift register
shift register
shift register
SPI Master
SPI Slave 0
SPI Slave n-1
33.6.3.4. Loop-Back Mode
For loop-back mode, configure the Data In Pinout (CTRLA.DIPO) and Data Out Pinout (CTRLA.DOPO) to
use the same data pins for transmit and receive. The loop-back is through the pad, so the signal is also
available externally.
33.6.3.5. Hardware Controlled SS
In master mode, a single SS chip select can be controlled by hardware by writing the Master Slave Select
Enable (CTRLB.MSSEN) bit to '1'. In this mode, the SS pin is driven low for a minimum of one baud cycle
before transmission begins, and stays low for a minimum of one baud cycle after transmission completes.
If back-to-back frames are transmitted, the SS pin will always be driven high for a minimum of one baud
cycle between frames.
, the time T is between one and two baud cycles depending on the SPI
transfer mode.
Atmel SAM L22G / L22J / L22N [DATASHEET]
Atmel-42402E-SAM L22G / L22J / L22N_Datasheet_Complete-07/2016
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