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copied!<p>The use of a shift register to multiplex (or de-multiplex, depending on your point of view) inputs/outputs is very common in digital electronics.</p> <p>Basically, you trade saving pins on your controller for having to include another chip (the shift register) in the design.</p> <p>In this case, the register works as a serial-to-parallel converter; it has a serial input line, which is fed with bits from your CPU. It also has 8 parallel outputs, connected to an 8-bit memory that is loaded serially from the CPU. Using this, you can "shift out" 8 bits of data on a single pin (plus one pin for clocking, typically), which are then stored in the shift register and can drive 8 LEDs in parallel.</p> <p>In this particular case, you need to figure out which AVR port pins the shift registers (the MBI5168 constant-current sink drivers contain the shift registers, here) are connected to. They ought to be chained to a pair of outputs, one for data and one for clock. Once you know those pins, you should be able to drive them yourself using the <a href="http://www.arduino.cc/en/Tutorial/ShiftOut" rel="nofollow noreferrer">ShiftOut</a> command.</p> <p>Digging a bit further, <a href="http://www.seeedstudio.com/depot/images/product/RaibowduinoCMD_Bata.rar" rel="nofollow noreferrer">this sample "sketch"</a> contains the following definitions, in the file called "Rainbow.h":</p> <pre><code>//MBI5168 #define SH_DIR_OE DDRC #define SH_DIR_SDI DDRC #define SH_DIR_CLK DDRC #define SH_DIR_LE DDRC #define SH_BIT_OE 0x08 #define SH_BIT_SDI 0x01 #define SH_BIT_CLK 0x02 #define SH_BIT_LE 0x04 #define SH_PORT_OE PORTC #define SH_PORT_SDI PORTC #define SH_PORT_CLK PORTC #define SH_PORT_LE PORTC </code></pre> <p>This is of course total digital "hearsay" (I don't own the device, I've never programmed on any kind of *duino), but I'd say this is the particle-spewing bullet delivery system you're looking for.</p> <p>I interpret this like so:</p> <ul> <li>PORTC is the one connected to the shift registers, all control pins are in PORTC.</li> <li>Four pins are dedicated (rather than the optimistic two I mentioned above).</li> <li>The clock is pin PORTC:2 and the data is PORTC:1.</li> </ul>

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