Measurement Computing PC104-DAC06 - Manual (Page 12)

A0 A1 A2 A3 A4 A5 A6 A7
0 1 2 3 4 5 6 7
Where the numbers along the top row are the bit positions within the 8-bit byte and
the numbers and symbols in the bottom row are the functions associated with that bit.
To write to or read from a register in decimal or HEX, the bit weights in table 2-1
apply:
Table 2-1. Bit Weights
80 128 7
40 64 6
20 32 5
10 16 4
8 8 3
4 4 2
2 2 1
1 1 0
HEX VALUE DECIMAL VALUE BIT POSITION
To write a control word or data to a register, the individual bits must be set to 0 or 1
then combined to form a byte.
The method of programming required to set/read bits from bytes is beyond the scope
of this manual.
In summary form, the registers and their function are listed in Table 2-2. Each
register has eight bits which constitute a byte of data or eight individual bit functions.
Each DAC has two 8-bit registers which are used to control it. The first register
contains the least-significant eight bits of D/A code. Write to it first.
D12
LSB
D11 D10 D9 D8 D7 D6 D5
0 1 2 3 4 5 6 7
The second register contains the most significant four bits of D/A code. Write to it
last. A write to this register will update the output of the D/A with all 12 bits of the
D/A code contained in the two registers. If the XFER jumper is set for the DAC, no
update will occur until a read of any one of the DAC registers is executed. Upon a
read, all DACs set for simultaneous transfer (XFER jumper set) will update together.
D4 D3 D2 D1
MSB
X X X X
0 1 2 3 4 5 6 7
8