MSB (Bit Order) Bit—The MSB bit controls the order in
which bits within a byte of data are read or written (either
most significant bit first or least significant bit first) as
follows:
Full-Scale Calibration Register (FCR)
The FCR is a 24-bit register which contains the full-scale
correction factor that is applied to the digital input before it
is transferred to the modulator. The contents of this register
will be the result of a self-calibration, or written to by the
user.
MSB
0
1
MSB-First
LSB-First
Default
The FCR is both readable and writable via the serial inter-
face. For applications requiring an accurate system calibra-
tion, a system calibration can be performed, the results
averaged, and a more precise value written back to the FCR.
MD1 - MD0 (Operating Mode) Bits—The Operating Mode
bits control the calibration functions of the DAC1220. The
Normal mode is used to perform conversions. The Self-
Calibration mode is a one-step calibration sequence that
calibrates both the offset and full scale.
The actual FCR value after calibration will change from part
to part and with configuration, temperature, and power
supply.
In addition, be aware that the contents of the FCR are not
used to directly correct the digital input. Rather, the correc-
tion is a function of the FCR value. This function is linear
and two known points can be used as a basis for interpolat-
ing intermediate values for the FCR. The contents of the
FCR are in unsigned binary format. This is not affected by
the DF bit in the Command register.
MD1
MD0
0
0
1
1
0
1
0
1
Normal Mode
Self-Cal
Sleep
X
Offset Calibration Register (OCR)
MSB
Byte 2
The OCR is a 24-bit register containing the offset correction
factor that is used to apply a correction to the digital input
before it is transferred to the modulator. The results of the
self-calibration process will be written to this register.
FCR23 FCR22 FCR21 FCR20 FCR19 FCR18 FCR17 FCR16
Byte 1
FCR15 FCR14 FCR13 FCR12 FCR11 FCR10 FCR9
FCR8
LSB
Byte 0
The OCR is both readable and writable via the serial inter-
face. For applications requiring a more accurate calibration,
a calibration can be performed, the results averaged, and a
more precise offset calibration value written back to the
OCR.
FCR7
FCR6
FCR5
FCR4
FCR3
FCR2
FCR1
FCR0
TABLE VII. Full-Scale Calibration Register.
Data Input Register (DIR)
The actual OCR value after calibration will change from part
to part and with configuration, temperature, and power supply.
The DIR is a 24-bit register which contains the digital input
value (see Table VIII). The register is latched on the falling
edge of the last bit of the last byte sent. The contents of the
DIR are then loaded into the modulator. This means that the
DIR register can be updated after sending 1, 2, or 3 bytes,
which is determined by the MB1 and MB0 bits in the
Instruction Register. The contents of the DIR can be Offset
Two’s Complement or Straight Binary.
In addition, be aware that the contents of the OCR are not
used to directly correct the digital input. Rather, the correc-
tion is a function of the OCR value. This function is linear
and two known points can be used as a basis for interpolat-
ing intermediate values for the OCR.
The results of calibration are averaged, Offset Two's Comple-
ment adjusted, and placed in the OCR.
MSB
Byte 2
MSB
Byte 2
OCR23 OCR22 OCR21 OCR20 OCR19 OCR18 OCR17 OCR16
DIR23
DIR22 DIR21 DIR20 DIR19 DIR18 DIR17
DIR16
Byte 1
Byte 1
OCR15 OCR14 OCR13 OCR12 OCR11 OCR10 OCR9
OCR8
LSB
DIR15
DIR7
DIR14 DIR13 DIR12 DIR11 DIR10
DIR9
DIR1
DIR8
LSB
DIR0
Byte 0
Byte 0
OCR7
OCR6
OCR5
OCR4
OCR3
OCR2
OCR1
OCR0
DIR6
DIR5
DIR4
DIR3
DIR2
TABLE VI. Offset Calibration Register.
TABLE VIII. Data Input Register.
®
9
BB [ BURR-BROWN CORPORATION ]
