The 12/8 pin determines whether the digital output data is to be organized as two 8-bit words (12/8 LOW) or a single 12-bit word (12/8 HIGH).
Data Bits 11 through 8. In the 12-bit format (see 12/8 and A0 pins), these pins provide the upper 4 bits of data. In the 8-bit format, they provide the upper 4 bits when A0 is LOW and are disabled when A0 is HIGH. Data Bits 7 through 4. In the 12-bit format these pins provide the middle 4 bits of data. In the 8-bit format they provide the middle 4 bits when Ao is LOW and all zeroes when A0 is HIGH. Data Bits 3 through 0. In the 12-bit format these pins provide the lower 4 bits of data. In the 8-bit format these pins provide the lower 4 bits of data when A0 is HIGH, they are disabled when A0 is LOW.