Toradex Colibri - Spi; SPI Signals; Unused SPI Signal Termination; Can

Colibri Carrier Board Design Guide
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2.11 SPI
The serial peripheral interface (SPI) bus is a synchronous, full-duplex interface. The Colibri module
form factor features one SPI interface. The interface has a chip select signal as a compatible
standard. Some modules may feature additional chip select signals or additional SPI interfaces as a
secondary function of other pins.
The clock polarity and phase of the SPI bus are not standardized. Some peripherals are latching
the data on the positive edge of the clock, while others are latching it at the negative edge. The SPI
modes describe these different behaviors. Ensure that the Colibri module and the peripheral device
can be set to the same SPI mode.
SPI Mode
Clock
Polarity
Clock
Phase
Description
0
0
0
The clock is positive polarity, and the data is latched on the positive edge of the SCK
1
0
1
The clock is positive polarity, and the data is latched on the negative edge of the SCK
2
1
0
The clock is negative polarity, and the data is latched on the positive edge of the SCK
4
1
1
The clock is negative polarity, and the data is latched on the negative edge of the SCK
Table 17: SPI Modes
2.11.1 SPI Signals
The SPI bus consists of one master and one or many slaves. In the Colibri standard, the module is
the SPI master. Some modules might allow being also used as SPI slaves. Some modules may
provide this function on different, non-standard pins.
Colibri
Pin
Colibri
Signal Name
I/O
Type
Power
Rail
Description
92
SPI_1_MOSI
O
CMOS
3.3V
Master Output, Slave Input
90
SPI_1_MISO
I
CMOS
3.3V
Master Input, Slave Output
86
SPI_1_CS0
O
CMOS
3.3V
Slave Select
88
SPI_1_CLK
O
CMOS
3.3V
Serial Clock
Table 18: SPI Signals
2.11.2 Unused SPI Signal Termination
Unused SPI signals can be left unconnected.
2.12 CAN
The Colibri form factor does not provide a controller area network (CAN) bus as a standard
interface. Some modules feature dedicated CAN interface signals. For the other modules, it is
recommended to add a CAN controller with an SPI interface on the carrier board to provide a CAN
interface. This section describes how to add a CAN controller to the SPI interface. If you intend to
use the dedicated CAN interface signals, please read the Colibri module's datasheet.
2.12.1 Reference Schematics
Besides a controller, the CAN interface requires a transceiver on the carrier board. Usually, the
CAN interface needs to be galvanically isolated from the Colibri computer module. There are
transceivers with integrated signal isolation couplers and isolated DC/DC converters available (for
example, the Analog Devices ADM3053). The other solution is to use separate components for the
transceiver, signal coupler, and DC/DC converter. There are different types of connectors used for
the CAN interface. The reference schematic below uses a DE-9 connector. Since this is not an
official standard, some devices might have a different pinout.