SPI Library Functions
SPI.begin()
Description
Initializes the SPI bus by setting SCK, MOSI, and SS to outputs, pulling SCK and MOSI low, and SS high.
Extended method for Arduino Due
If
you specify one of the Arduino Due's Slave Select (SS) pin in the call
to SPI.begin(), the pin is configured to be directly managed by the SPI
interface.
Note that once the pin is configured, you can't
use it anymore as a general I/O, unless you call the SPI.end() method
on the same pin.
The only pins that can be configured to be managed by SPI interface are the Arduino Due's Slave Select pins: 4, 10, 52 and 78.
Syntax
| SPI.begin() | |
| SPI.begin(slaveSelectPin) | (Arduino Due only) |
Parameters
| slaveSelectPin: | slave device SS pin | (Arduino Due only) |
Returns
None
SPI.end()
Description
Disables the SPI bus (leaving pin modes unchanged).
Extended method for Arduino Due
If
you specify one of the Arduino Due's Slave Select (SS) pin in the call
to end(), the specified pin is disconnected from the SPI interface and
is available again as a general I/O.
Syntax
| SPI.end() | |
| SPI.end(slaveSelectPin) | (Arduino Due only) |
Parameters
| slaveSelectPin: | slave device SS pin | (Arduino Due only) |
Returns
None
SPI.setBitOrder()
Description
Sets the order of the bits shifted out of and into the SPI bus,
either LSBFIRST (least-significant bit first) or MSBFIRST
(most-significant bit first).
Extended method for Arduino Due
If
you specify one of the Arduino Due's Slave Select (SS) pin in the call
to setBitOrder(), the bit order setting is applied only to the device
connected to the specified SS pin.
Syntax
| SPI.setBitOrder(order) | |
| SPI.setBitOrder(slaveSelectPin, order) | (Arduino Due only) |
Parameters
order: either LSBFIRST or MSBFIRST
Returns
None
SPI.setClockDivider()
Description
Sets the SPI clock divider relative to the system clock. On AVR
based boards, the dividers available are 2, 4, 8, 16, 32, 64 or 128.
The default setting is SPI_CLOCK_DIV4, which sets the SPI clock to
one-quarter the frequency of the system clock (4 Mhz for the boards at
16 MHz).
Arduino Due
On the Due, the system clock can be divided by values from 1 to 255. The default value is 21, which sets the clock to 4 MHz like other Arduino boards.
Extended method for Arduino Due
If
you specify one of the Arduino Due's Slave Select (SS) pin in the call
to setClockDivider(), the clock setting is applied only to the device
connected to the specified SS pin.
Syntax
| SPI.setClockDivider(divider) | |
| SPI.setClockDivider(slaveSelectPin, divider) | (Arduino Due only) |
Parameters
| divider: |
| (On AVR boards) |
| slaveSelectPin: | slave device SS pin | (Arduino Due only) |
| divider: | a number from 1 to 255 | (Arduino Due only) |
Returns
None
SPI.setDataMode()
Description
Sets the SPI data mode: that is, clock polarity and phase. See the Wikipedia article on SPI for details.
Extended method for Arduino Due
If
you specify one of the Arduino Due's Slave Select (SS) pin in the call
to setDataMode(), the data mode setting is applied only to the device
connected to the specified SS pin.
Syntax
| SPI.setDataMode(mode) | |
| SPI.setDataMode(slaveSelectPin, mode) | (Arduino Due only) |
Parameters
| mode: |
| |
| slaveSelectPin | slave device SS pin | (Arduino Due only) |
Returns
None
SPI.transfer()
Description
Transfers one byte over the SPI bus, both sending and receiving.
Extended method for Arduino Due
If
you specify one of the Arduino Due's Slave Select (SS) pin in the call
to SPI.transfer(), the specified pin is activated (pulled low) before
the transfer occurs and deactivated (pulled high) when the transfer is
finished.
You can use an additional SPI_CONTINUE or
SPI_LAST parameter to manage the Slave Select line after the transfer.
SPI_CONTINUE keeps the specified SS pin active (low) after the transfer
to allow the send of additional bytes via the transfer() function in the
same SPI transaction. The last byte to be transferred
should be accompanied by the SPI_LAST parameter. By default, if you
don't specify a third parameter, SPI_LAST is used. When a transfer is
complete with SPI_LAST, the slave select pin returns inactive (high).
Syntax
| SPI.transfer(val) | |
| SPI.transfer(slaveSelectPin, val) | (Arduino Due only) |
| SPI.transfer(slaveSelectPin, val, transferMode) | (Arduino Due only) |
Parameters
| val: | the byte to send out over the bus | |
| slaveSelectPin: | slave device SS pin | (Arduino Due only) |
| transferMode: |
| (Optional, Arduino Due only) |
Returns
the byte read from the bus.
