CONFIG SPI

Action

Configures the SPI related statements.

Syntax for software SPI

CONFIG SPI = SOFT, DIN = PIN, DOUT = PIN , SS = PIN|NONE, CLOCK = PIN , SPIIN=value

Syntax for hardware SPI

Remarks

SPI	SOFT for software emulation of SPI, this allows you to choose the PINS to use. Only works in master mode. HARD for the internal SPI hardware, that will use fixed pins of the microprocessor.
DIN	Data input or MISO. Pin is the pin number to use such as PINB.0
DOUT	Data output or MOSI. Pin is the pin number to use such as PORTB.1
SS	Slave Select. Pin is the pin number to use such as PORTB.2 Use NONE when you do not want the SS signal to be generated. See remarks
CLOCK	Clock. Pin is the pin number to use such as PORTB.3
DATA ORDER	Selects if MSB or LSB is transferred first.
MASTER	Selects if the SPI is run in master or slave mode.
POLARITY	Select HIGH to make the CLOCK line high while the SPI is idle. LOW will make clock LOW while idle.
PHASE	Refer to a data sheet to learn about the different settings in combination with polarity.
CLOCKRATE	The clock rate selects the division of the of the oscillator frequency that serves as the SPI clock. So with 4 you will have a clock rate of 4.000000 / 4 = 1 MHz , when a 4 MHZ XTAL is used.
NOSS	1 or 0. Use 1 when you do not want the SS signal to be generated in master mode.
INTERRUPT	Specify ON or OFF. ON will enable the SPI interrupts to occur. While OFF disables SPI interrupts. ENABLE SPI and DISABLE SPI will accomplish the same.
SPIIN	When reading from the SPI slave, it should not matter what kind of data you send. But some chips require a value of 255 while others require a value of 0. By default, when the SPIIN option is not provided, a value of 0 will be sent to the SPI slave. With this SPIIN option you can override this value.

The default setting for hardware SPI when set from the Compiler, Options, SPI menu is MSB first, POLARITY = HIGH, MASTER = YES, PHASE = 0, CLOCKRATE = 4

When you use CONFIG SPI = HARD alone without the other parameters, the SPI will only be enabled. It will work in slave mode then with CPOL =0 and CPH=0.

In hardware mode the SPIINIT statement will set the SPI pins to :

sbi DDRB,7 ; SCK output

cbi DDRB,6 ; MISO input

sbi DDRB,5 ; MOSI output

In softmode the SPIINIT statement will set the SPI pins for example to :

sbi PORTB,5 ;set latch bit hi (inactive)SS

sbi DDRB,5 ;make it an output SS

cbi PORTB,4 ;set clk line lo

sbi DDRB,4 ;make it an output

cbi PORTB,6 ;set data-out lo MOSI

sbi DDRB,6 ;make it an output MOSI

cbi DDRB,7 ;MISO input

Ret

When you want to address multiple slaves with the software SPI you need multiple pins to select/activate the slave chip. Specify NONE for SS in that case. This also means that before every SPI command you need to set the logic level to 0 to address the chip and after the SPI command you need to set it back to a logic high level.

The hardware SPI also has this option. The NOSS parameter with a value of 1, will not set the SS line to logic 0 when the SPI operation begins. You need to set SS or any other pin of your choice to a logic 0 yourself. After the SPI command(s) are used you need to set it back to a logic 1 to deselect the slave chip.

All SPI routines are SPI-master routines. Example 2 below demonstrates how to create a soft SPI slave. In the samples directory you will also find a SPI hardware master and SPI hardware slave sample.