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- ===================================================
- spi_butterfly - parport-to-butterfly adapter driver
- ===================================================
- This is a hardware and software project that includes building and using
- a parallel port adapter cable, together with an "AVR Butterfly" to run
- firmware for user interfacing and/or sensors. A Butterfly is a $US20
- battery powered card with an AVR microcontroller and lots of goodies:
- sensors, LCD, flash, toggle stick, and more. You can use AVR-GCC to
- develop firmware for this, and flash it using this adapter cable.
- You can make this adapter from an old printer cable and solder things
- directly to the Butterfly. Or (if you have the parts and skills) you
- can come up with something fancier, providing circuit protection to the
- Butterfly and the printer port, or with a better power supply than two
- signal pins from the printer port. Or for that matter, you can use
- similar cables to talk to many AVR boards, even a breadboard.
- This is more powerful than "ISP programming" cables since it lets kernel
- SPI protocol drivers interact with the AVR, and could even let the AVR
- issue interrupts to them. Later, your protocol driver should work
- easily with a "real SPI controller", instead of this bitbanger.
- The first cable connections will hook Linux up to one SPI bus, with the
- AVR and a DataFlash chip; and to the AVR reset line. This is all you
- need to reflash the firmware, and the pins are the standard Atmel "ISP"
- connector pins (used also on non-Butterfly AVR boards). On the parport
- side this is like "sp12" programming cables.
- ====== ============= ===================
- Signal Butterfly Parport (DB-25)
- ====== ============= ===================
- SCK J403.PB1/SCK pin 2/D0
- RESET J403.nRST pin 3/D1
- VCC J403.VCC_EXT pin 8/D6
- MOSI J403.PB2/MOSI pin 9/D7
- MISO J403.PB3/MISO pin 11/S7,nBUSY
- GND J403.GND pin 23/GND
- ====== ============= ===================
- Then to let Linux master that bus to talk to the DataFlash chip, you must
- (a) flash new firmware that disables SPI (set PRR.2, and disable pullups
- by clearing PORTB.[0-3]); (b) configure the mtd_dataflash driver; and
- (c) cable in the chipselect.
- ====== ============ ===================
- Signal Butterfly Parport (DB-25)
- ====== ============ ===================
- VCC J400.VCC_EXT pin 7/D5
- SELECT J400.PB0/nSS pin 17/C3,nSELECT
- GND J400.GND pin 24/GND
- ====== ============ ===================
- Or you could flash firmware making the AVR into an SPI slave (keeping the
- DataFlash in reset) and tweak the spi_butterfly driver to make it bind to
- the driver for your custom SPI-based protocol.
- The "USI" controller, using J405, can also be used for a second SPI bus.
- That would let you talk to the AVR using custom SPI-with-USI firmware,
- while letting either Linux or the AVR use the DataFlash. There are plenty
- of spare parport pins to wire this one up, such as:
- ====== ============= ===================
- Signal Butterfly Parport (DB-25)
- ====== ============= ===================
- SCK J403.PE4/USCK pin 5/D3
- MOSI J403.PE5/DI pin 6/D4
- MISO J403.PE6/DO pin 12/S5,nPAPEROUT
- GND J403.GND pin 22/GND
- IRQ J402.PF4 pin 10/S6,ACK
- GND J402.GND(P2) pin 25/GND
- ====== ============= ===================
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