AD7809_15 Datasheet, PDF (14/28 Pages) Analog Devices – 3.3 V to 5 V Quad/Octal 10-Bit DACs

AD7804/AD7805/AD7808/AD7809
Table IVb. AD7809 DAC Data/Control Register
Selection Table
MODE A2 A1
0
0
0
0
0
0
0
0
1
0
0
1
0
1
0
0
1
0
0
1
1
0
1
1
1
0
0
1
0
0
1
0
1
1
0
1
1
1
0
1
1
0
1
1
1
1
1
1
A0 Function Selected
0
DAC A Control Register
1
DAC B Control Register
0
DAC C Control Register
1
DAC D Control Register
0
DAC E Control Register
1
DAC F Control Register
0
DAC G Control Register
1
DAC H Control Register
0
DAC A Data Register
1
DAC B Data Register
0
DAC C Data Register
1
DAC D Data Register
0
DAC E Data Register
1
DAC F Data Register
0
DAC G Data Register
1
DAC H Data Register
AD7805/AD7809 SYSTEM OR CHANNEL CONTROL
REGISTER SELECTION
MD0
0
This enables writing to the system control register.
The contents of this are shown in Figure 12. Mode
must be low to access this control register.
1
This enables writing to the channel control register.
The contents of this are shown in Figure 13. Mode
must also be low to access this control register.
AD7805/AD7809 SYSTEM CONTROL REGISTER
The bits in this register allow control over all DACs in the pack-
age. The control bits include data format (10/8), power down
(PD), DAC input coding select (BIN/COMP), system standby
(SSTBY) and a system clear (SCLR). The function of these bits
is as follows:
Data Format
10/8
0
10-bit parallel loading structure.
1
Byte loading structure. (8+2 loading).
Input Coding
BIN/COMP
0
Twos complement coding.
1
Offset Binary Coding.
Power Down
PD
0
Complete power-down of device.
1
Normal operation (default on power-up).
System Standby
SSTBY
0
Normal operation.
1
All DACs in the package put in standby mode (default
on power-up).
System Clear
SCLR
0
Normal operation.
1
All DACs in the package are cleared to a known state
depending on the coding scheme selected. The SCLR bit
clears the Main DACs only; the Sub DACs are unaf-
fected by the system clear function. The main DAC is
cleared to different levels depending on the coding
scheme. With offset binary coding the Main DAC output
is cleared to the bottom of the transfer function V_BIAS/16.
With twos complement coding the Main DAC output is
cleared to midscale V_BIAS. The channel output will be the
sum of the Main DAC and Sub DAC contributions.
AD7805/AD7809 CHANNEL CONTROL REGISTER
This register allows the user to have control over individual
DACs in the package. The control bits in this register include
multiplexer output selection (MX1 and MX0), Main or Sub
DAC selection (MAIN/SUB), standby (STBY) and individual
DAC clear (CLR). The function of these bits is as follows.
Multiplexer Selection (MX1, MX0)
Table V shows the V_BIAS selection using MX1 and MX0 bits in
the channel control register.
Table V. V_BIAS Selection Table
MX1
0
0
1
1
MX0
0
1
0
1
V_BIAS
V_DD/2 (Default on Power-Up)
INTERNAL VREF
REFIN
Undetermined
Main DAC or Sub DAC Selection
MAIN/SUB
0
Writing a 0 to this bit means that the data in the next
data register write is transferred to the selected Main
DAC.
1
Writing a 1 to this bit means that the data in the next
data register write is transferred to the selected Sub DAC.
This applies to the 10-bit parallel load feature. In byte
load mode, (Figure 15) DB0 selects the Main or Sub
DAC data registers.
Standby
STBY
0
Places the selected DAC and its associated linear cir-
cuitry in Standby Mode.
1
Normal operation (default on power-up).
Clear
CLR
0
Normal operation.
1
Clears the output of the selected Main DAC to one
of two conditions depending on the input coding se-
lected. With offset binary coding the Main DAC out-
put is cleared to the bottom of the transfer function,
V_BIAS/16 and with twos complement coding the Main
DAC output is cleared to midscale V_BIAS. The Sub
DAC is unaffected by a clear operation. An LDAC
signal has to be applied to the DAC for a channel clear
to be implemented.
–14–
REV. A