ADLINK ACL-8111 - Manual (Page 37)

Operation Theorem • 31
Note that the D/A registers are "double buffered", so that the D/A analog
output signals will not be updated until the high byte is written. When write 12
bits data to D/A registers of the ACL-8111, the low byte must be written
before the high byte. This procedure can insure a single step transition when
the D/A conversion.
Note: when writing digital data to D/A register, the low byte data should
be written first, because the register will temporarily hold and not
released to output. After the high byte is written, both high and low
will add and passed to A/D converter.