Latest revision as of 20:13, 17 January 2017

Action

Configures the SPI related statements.

Syntax for software SPI

CONFIG SPI|SPISOFT = SOFT, DIN = PIN, DOUT = PIN , SS = PIN|NONE, CLOCK = PIN , SPIIN=value , MODE=mode, speed=speed, setup=setup

Syntax for hardware SPI

CONFIG SPI|SPIHARD = HARD, INTERRUPT=ON|OFF, DATA_ORDER = LSB|MSB , MASTER = YES|NO , POLARITY = HIGH|LOW , PHASE = 0|1, CLOCKRATE = 4|16|64|128 , NOSS=1|0 , SPIIN=value

When you just want to use one SPI slave chip using the HW SPI, use this : Config Spi = Hard , Interrupt = Off , Data_Order = Msb , Master = Yes , Polarity = Low , Phase = 0 , Clockrate = 128

When you want more details, read more about the details and options below.

Remarks software SPI

Software SPI allows you to chose the processor pins for the SPI operation. Typically you need a MISO, MOSI, CLOCK and SS pin.

While this is an advantage, the disadvantage is that software SPI uses more processor resources.

In software spi mode the SPIINIT statement will set the SPI pins to the proper logic level. 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

This is just an example. The actual code differs from processor to processor. And also depends on the used port pins.

In most cases, there is just one slave chip to control/address. In such a case you need only one slave select(SS) pin to control this chip. But SPI can also be used to control multiple SPI slaves.

These slaves need to use the same mode. You can not dynamically change the SPI mode at run time.

BASCOM will automatically set the SS pin to logic level 0 when you use a SPI command. And when the SPI command has executed, it will set the SS pin back to a logic 1.

When the slave chip has in inverted SS pin (it requires a 1 to be active) you can not use this automatic SS signal generation.

When you want to address multiple slaves with the software SPI you need multiple pins to select the different slave chips. In this case you also can not use the automatic SS signal generation.

The solution is to specify NONE for SS. This will eliminate the automatic SS signal generation. But it also means that you as a user need to handle this. In practice this means :

- choose a port pin to serve as SS pin

- set it to output and to the right logic level (1 in most cases to disable the slave)

- before using a SPI statement, select the slave by making SS logic 0.

- after the SPI statement, set the SS logic level back to 1.

Example user controlled SS pin.

Config Spi = Soft , Din = Pinb.0 , Dout = Portb.1 , Ss = NONE , Clock = Portb.3
MySS alias portb.2
Config MySS=OUTPUT : MySS=1 ' deactivate
Dim var As Byte
SPIINIT                     ' Init SPI state and pins.
MySS=0                     ' select SS
SPIOUT var , 1             ' send 1 byte
MySS=1                     ' deselect SS

Remarks Hardware SPI

Hardware SPI is the best option when it is available. Hardware SPI can be used in master and slave mode. All BASCOM SPI statements are master mode routines.

The only disadvantage is that you must use the dedicated hardware pins, the SS pin included!

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

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

SCK = Ouput

MISO = Input

MOSI = Output 

In Master mode, the SS pin will be set to output too.

As explained for Software SPI, it is not always desirable to use the SS pin to control the SPI slave chip. Because you want to use a different pin, use multiple slave, or the slaves has an inverted SS signal.

Since the hardware SPI always has an SS pin, there is an override for this with a different name than for soft spi : NOSS=0|1

So where SS=NONE is used for SOFT SPI to disable automatic SPI signal generation, the HARDWARE SPI use the option NOSS=1 to do the same. NOSS means NO SS signal generation.

When NOSS is not used or NOSS=0, the default will be used where the dedicated SS pin will create the slave select signals.

One big difference with software SPI, is that in order to use the SPI in master mode, the SS pin must be set to output mode. Even if you do not use the dedicated SS pin to control a SPI slave chip !

When the SS pin is in input mode, a logic 0 at the input will turn the master mode into slave mode. A pull up resistor could do the same but our advise : use the SS pin as an output pin.

The SS pin is set to output mode when the MASTER mode is selected. So even if NOSS=1, the SS pin is set to output mode when MASTER=YES.

When using NOSS=1 : In order to use the Hardware SPI in master mode, you need to set the SS pin to output. In input mode, this pin can be used to set the SPI bus into slave mode. You only need to set the pin to output when you use theNOSS=1 option. With NOSS=0, the compiler will set the SS pin to output and makes SS pin logic 1.

When NOSS=1 is used, the SS pin is only made an output pin in MASTER mode. No logic level is set when NOSS=1.

This table show how SS pin is set with the various options for HW mode.

All SPI routines are SPI-master routines. In the samples directory you will also find a SPI hardware master and SPI hardware slave sample.

The SPI protocol is explained in the chapter : Using the SPI protocol

When using a processor for both the master and slave : Take in mind that the SPI master processor clock frequency must be 1/4 of the SPI slave processor frequency.

Chips with 2 full SPI ports

Some new processors like the ATMEGA328PBhave 2 SPI ports. In order to use this second SPI port you have to add a '1' to the statement.

CONFIG SPI becomes CONFIG SPI1

SPIIN becomes SPIIN1

SPIOUT becomes SPIOUT1

SPIINIT becomes SPI1INIT

SPIMOVE becomes SPI1MOVE

See also

SPIIN , SPIOUT , SPIINIT , SPI , SPIMOVE

Example for Software SPI

Config Spi = Soft , Din = Pinb.0 , Dout = Portb.1 , Ss = Portb.2 , Clock = Portb.3
Dim var As Byte
SPIINIT 'Init SPI state and pins.
SPIOUT var , 1 'send 1 byte

Example for Hardware SPI

Config Spi = Hard , Interrupt = Off , Data Order = Msb , Master = Yes , Polarity = High , Phase = 1 , Clockrate = 4 , Noss = 1
Spiinit