mcp4131 and attiny85

Projects Networking, Protocols, and Devices
4

In that case:

int command_data; upper 4-6 bits are command related, lower 10 are data

digitalWrite (CS, LOW);
shiftout ( dataPin, clockPin, MSBFIRST, highByte (command_data) );
shiftout ( dataPin, clockPin, MSBFIRST, lowByte (command_data) );
digitalWrite (CS, HIGH);