The serial interface is double buffered: a 12-bit input shift register is followed by four 8-bit buffer registers and four 8-bit DAC registers. The 12-bit serial word consists of eight data bits and four control bits (for DAC selection and special programming commands). Both the input and DAC registers can be updated independently or simultaneously with a single software command. Two additional asynchronous control pins, LDAC and CLR, provide simultaneous updating or clearing of the input and DAC registers.