Bit-banging Ethernet On An ATTiny85

Ethernet bit banging

[Cnlohr] just published an ingenious but dangerous way to send Ethernet packets using an ATTiny85. The ATtiny directly drives one pair of differential TX wires of a standard Ethernet cable. Doing so will force the TX signal ground to be the same as the ATTiny’s and in some cases may put 48V on your AVR if your cable is plugged into a Power Over Ethernet switch… which may be a problem.

In the video embedded below [cnlhor] explains that the microcontroller is clocked at 20Mhz to bit-bang the Manchester encoded electrical signals. Using a neat trick his home switch will detect his platform as a 10MBit Ethernet switch which can then send hard-coded packets to his computer. As you can guess, each of this packets takes quite a bit of space inside the ATTiny’s flash memory: 2+Kbytes. All of the code used may be downloaded on the creator’s GitHub repository, though he constantly warned us that it shouldn’t be used for real life applications.

Edit: One of our readers also let us know of a similar awesome project called the IgorPlug-UDP. Make sure to check it out!

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Learn JTAG by writing a bit-banging programmer

j-tag-flow-chart

[Pesco] won one of Dangerous Prototypes’ PCB giveaways a few months ago. He opted for a CPLD breakout board. He just needed to put in a parts order and populate the components himself. But then what? He needed a JTAG programmer to work with the chip. Like any good autodidact he choose to make his own rather than buying one. He absorbed the JTAG specification and coded a bit banging programmer using an Arduino.

We’ve used JTAG many times to program ARM chips. But until now we never took the time to figure out how the specification works. If you’ve got an IEEE subscription you can download the whitepaper, but [Pesco] was also able to find one floating around on the interwebs. The flow chart on the left is the cheat sheet he put together based on his readings. From there he wrote the Arduino sketch which implements the programming standard, allowing him to interact with a chip through a minicom terminal window.

[via Dangerous Prototypes]

Bit banging through a USB parallel port adapter

bit-banging-through-a-usb-parallel-port-adapter

If you’ve ever looked into low-level parallel port access you may have learned that it only works with actual parallel port hardware, and not with USB parallel port adapters. But here’s a solution that will change your thinking. It borrows from the way printers communicate to allow USB to parallel port bit banging without a microcontroller.

Sure, adding a microcontroller would make this dead simple. All you need to do is program the chip to emulate the printer’s end of the communications scheme. But that’s not the approach taken here. Instead the USB to RS232 (serial) converter also pictured above is used as a reset signal. The strobe pin on the parallel port drives an inverter which triggers a thyristor connected to the busy pin. Thyristors are bistable switches so this solution alone will never clear the busy pin. That’s where the serial connection comes into play. By alternating the data transmitted from the computer between the bit-bang values sent to LP0 and 0xF0 sent to the serial connector the eight parallel data bits become fully addressable. See the project in action in the clip after the break.

Bit banging VGA from an SD card slot

If you’ve got some favorite electronic device that includes an SD card slot but doesn’t have a video out port you may be able to push VGA signals through the card reader conductors. That’s exactly what’s going on above with the Ben NanoNote, a sub-$100 Linux device which we’ve seen using its SD card slot as general I/O before.

The hardware to capture the signals includes a breakout board for the card slot. Free-formed on the other end of that connector card is a gaggle of resistor which handle level conversion for the VGA color signals, with a VGA cable taking it from there to the monitor. The software that makes this happen is a dirty hack, blocking all other functions while it displays a still image. But we’re sure that it can be cleaned up somewhat. Just don’t hold out hopes for full-motion video, this little guy just doesn’t have it in him.

[via Dangerous Prototypes via Slashdot]

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