MCP4728_DAC_H_MASK
FIELD_PREP(MCP4728_DAC_H_MASK, ch->dac_value >> 8);
outbuf[1] |= FIELD_PREP(MCP4728_DAC_H_MASK, ch->dac_value >> 8);
ch->dac_value = FIELD_GET(MCP4728_DAC_H_MASK, r2) << 8 |