170
Boards
© Tibbo Technology Inc.
·
Generate 23 additional clock pulses, every time setting the next bit on the DO line
while the CLOCK is at LOW.
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Set the TFS line HIGH. The write is complete.
A/D converter initialization
If you refer to the data sheet for the AD7712 you will find that there are many
configuration options. Without resorting to reprinting the data sheet, we provide the
following brief info:
bit2
3
bit2
2
bit2
1
bit2
0
bit1
9
bit1
8
bit1
7
bit1
6
bit1
5
bit1
4
bit1
3
bit1
2
MD
2
MD
1
MD
0
G2
G1
G0
CH
PD
WL
X
BO
BU
bit1
1
bit1
0
bit9
bit8
bit7
bit6
bit5
bit4
bit3
bit2
bit1
bit0
FS1
1
FS1
0
FS9
FS8
FS7
FS6
FS5
FS4
FS3
FS2
FS1
FS0
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The MD2-0 field is set to 000 for normal operation or 001 for self-calibration.
There are also other configuration modes available, but they are not supported by
the IB1004.
·
The G2-0 field defines the gain of the A/D. The signal measured by the A/D is pre-
amplified according to this gain. Writing 000 will select the gain of 1, 001- the gain
of 2,... 111- the gain if 128.
·
The CH field selects the channel and has to be set to 1 for the IB1004 to work
properly. This channel selection should not be confused with the IB1004 input
channel selector described above.
·
The PD power down bit should be at 0.
·
The WL word length bit should be at 0 for 16-bit resolution (sufficient for most
applications), or at 1 for 24-bit resolution.
·
The BO burnout current bit should be at 0.
·
The B/U bit should be at 0 to select bipolar operation.
·
The FS11-0 filter selection bits that should be set according to the requirements
of your application. We often use the value of 4E Hex. Read page 10 of the IC's
datasheet and you will find out that this corresponds with the data rate of 250Hz
(times/second) and the effective resolution of 15 bits. We choose this as a good
compromise between the speed and resolution. We choose the resolution of 15
bits because the D/A portion of the product has the resolution of 14 bits.
To initialize the A/D converter, write the desired configuration word on startup. For
the 15-bit effective resolution described above write the hex value of 22004E. This
will set up the converter and kick-off a self-calibration process (see below).
Optional self-calibration
The A/D converter will operate at a better precision if you calibrate it first. Set bits
MD2-0 of the configuration register to 001 to start self-calibration. Self-calibration,
as the name implies, is an automatic process that does not require any external
intervention. The calibration takes time. To determine when the calibration is over,
poll the DI line after writing to the configuration register: