Hi,

The datasheet says that the oscillator input freq. range is between 2.9 and 6.1 MHz. So using the internal oscillator @ 4Mhz will give you a clock out at 1MHz.(Instruction cycle clock). You can use an external crystal oscillator @4MHz and buffer the oscout pin to feed into your allegro chip. Since the data is 20 bit MSB first, the possibility of Shiftout rules out. Keep the different controls in different bytes and use your own routine to dump the data. It should be easy in a for-next loop doing a clock toggle at around 100uS and dumping the databits. Since each instruction clock cycle at 4MHz takes 1uS it will be better to use a slower clock so that your overall timing are not effected by other tasks (like getting individual bits and dumping to the data line). Remember to start the operation with the Strobe line.

Regards

Sougata