shurru / tinyspi

Arduino hardware SPI library for ATtiny44/84/45/85

#Arduino tinySPI Library http://github.com/JChristensen/tinySPI
ReadMe file
Jack Christensen Oct 2013

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##Description tinySPI is an Arduino SPI master library for ATtiny44/84/45/85 that utilizes the USI hardware in the ATtiny MCUs.

Because the USI hardware is not as sophisticated as the dedicated SPI hardware in the ATmega MCUs, tinySPI is more limited than the standard Arduino SPI library but still has several advantages over software bit-bang approaches.

As compared to the Arduino shiftOut() function, tinySPI

• is about 15 times faster,
• has a smaller program memory footprint, and
• has a consistent bit clock period.

tinySPI does not support

• sending least-significant bit first,
• SPI data modes 2 and 3, or
• various SPI clock frequencies.

tinySPI will generate an SPI bit clock that is about one-tenth the MCU system clock frequency. For example, given a 1MHz system clock, the SPI clock will be about 100kHz, and it will take about 80µs to transfer one byte.

Interrupts are inhibited during each byte transfer to ensure a consistent bit clock period.

Included with the library are example sketches that demonstrate driving a 74HC595 shift register from an ATtiny84 and from an ATtiny85.

tinySPI was developed with Arduino 1.0.5 and the Arduino-Tiny ATtiny core 0100-0017.

##Methods

• begin()
• end()
• setDataMode()
• transfer()

###begin() #####Description Initializes the SPI bus, sets the USCK and DO pins to outputs, sets the DI pin to input. #####Syntax SPI.begin(); #####Parameters None. #####Returns None.

###end() #####Description Disables the SPI bus (leaving the pin modes unchanged). #####Syntax SPI.end(); #####Parameters None. #####Returns None.

###setDataMode() #####Description Sets the SPI data mode, i.e. clock polarity and phase. See the Wikipedia article on SPI for details. #####Syntax SPI.setDataMode(mode) #####Parameters mode: SPI_MODE0 or SPI_MODE1 (modes 2 and 3 are not supported) #####Returns None.

###transfer() #####Description Transfers one byte over the SPI bus, both sending and receiving. Interrupts are inhibited during each byte transfer to ensure a consistent bit clock period. #####Syntax SPI.transfer(val); #####Parameters val: the byte to send over the bus (byte) #####Returns the byte read from the bus (byte)