The actual image shows Hijack reading the current temperature from the empeg's ds1821 temperature sensor chip over a one-wire bus.
First Hijack pulls the DQ line low for a minimum of 480us, then tristates it again. The chip waits 15-60us, then pulses the line low to indicate presence. Hijack then strobes out the command, 0xAA in this case. The chip then responds with the current temperature reading.
Freaky. I've done a lot of 1 wire stuff over the past year, including the ds1821, various battery monitors and the SHA-1 iButtons for secure applications!
The processor I that I generally use (AT91SAM7S256) has the option to enable open drain on every IO pin, which is uber-handy for 1 wire. Just use the normal UART but open drain the TX and tie TX/RX together and you lose all the timing overheard by getting the uart to do it all for you!
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