Datasheet

DAC108S085
www.ti.com SNAS423B –AUGUST 2007–REVISED MARCH 2013
SERIAL INPUT REGISTER
The DAC108S085 has two modes of operation plus a few special command operations. The two modes of
operation are Write Register Mode (WRM) and Write Through Mode (WTM). For the rest of this document, these
modes will be referred to as WRM and WTM. The special command operations are separate from WRM and
WTM because they can be called upon regardless of the current mode of operation. The mode of operation is
controlled by the first four bits of the control register, DB15 through DB12. See Table 1 for a detailed summary.
Table 1. Write Register and Write Through Modes
DB[15:12] DB[11:0] Description of Mode
WRM: The registers of each DAC Channel can be written to without causing
1 0 0 0 X X X X X X X X X X X X
their outputs to change.
1 0 0 1 X X X X X X X X X X X X WTM: Writing data to a channel's register causes the DAC output to change.
When the DAC108S085 first powers up, the DAC is in WRM. In WRM, the registers of each individual DAC
channel can be written to without causing the DAC outputs to be updated. This is accomplished by setting DB15
to "0", specifying the DAC register to be written to in DB[14:12], and entering the new DAC register setting in
DB[11:0] (see Table 2).The DAC108S085 remains in WRM until the mode of operation is changed to WTM. The
mode of operation is changed from WRM to WTM by setting DB[15:12] to "1001". Once in WTM, writing data to a
DAC channel's register causes the DAC's output to be updated as well. Changing a DAC channel's register in
WTM is accomplished in the same manner as it is done in WRM. However, in WTM the DAC's register and
output are updated at the completion of the command (see Table 2). Similarly, the DAC108S085 remains in
WTM until the mode of operation is changed to WRM by setting DB[15:12] to "1000".
Table 2. Commands Impacted by WRM and WTM
DB15 DB[14:12] DB[11:0] Description of Mode
WRM: D[11:0] written to ChA's data register only
0 0 0 0 D11 D10 ... D2 X X
WTM: ChA's output is updated by data in D[11:0]
WRM: D[11:0] written to ChB's data register only
0 0 0 1 D11 D10 ... D2 X X
WTM: ChB's output is updated by data in D[11:0]
WRM: D[11:0] written to ChC's data register only
0 0 1 0 D11 D10 ... D2 X X
WTM: ChC's output is updated by data in D[11:0]
WRM: D[11:0] written to ChD's data register only
0 0 1 1 D11 D10 ... D2 X X
WTM: ChD's output is updated by data in D[11:0]
WRM: D[11:0] written to ChE's data register only
0 1 0 0 D11 D10 ... D2 X X
WTM: ChE's output is updated by data in D[11:0]
WRM: D[11:0] written to ChF's data register only
0 1 0 1 D11 D10 ... D2 X X
WTM: ChF's output is updated by data in D[11:0]
WRM: D[11:0] written to ChG's data register only
0 1 1 0 D11 D10 ... D2 X X
WTM: ChG's output is updated by data in D[11:0]
WRM: D[11:0] written to ChH's data register only
0 1 1 1 D11 D10 ... D2 X X
WTM: ChH's output is updated by data in D[11:0]
As mentioned previously, the special command operations can be exercised at any time regardless of the mode
of operation. There are three special command operations. The first command is exercised by setting data bits
DB[15:12] to "1010". This allows a user to update multiple DAC outputs simultaneously to the values currently
loaded in their respective control registers. This command is valuable if the user wants each DAC output to be at
a different output voltage but still have all the DAC outputs change to their appropriate values simultaneously
(see Table 3).
The second special command allows the user to alter the DAC output of channel A with a single write frame.
This command is exercised by setting data bits DB[15:12] to "1011" and data bits DB[11:0] to the desired control
register value. It also has the added benefit of causing the DAC outputs of the other channels to update to their
current control register values as well. A user may choose to exercise this command to save a write sequence.
For example, the user may wish to update several DAC outputs simultaneously, including channel A. In order to
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