ADUC814 Analog Devices, ADUC814 Datasheet - Page 29

• Manufacturer Part Number: ADUC814
• Description: Precision Analog Microcontroller: 1.3MIPS 8052 MCU + 8kB Flash + 6-Ch 12-Bit ADC + Dual 12-Bit DAC
• Manufacturer: Analog Devices

Specifications of ADUC814

• Mcu Core: 8052
• Mcu Speed (mips): 1.3
• Sram (bytes): 256Bytes
• Gpio Pins: 17
• Adc # Channels: 6

gain coefficient compensates for a larger analog input signal
range and scales down the ADC transfer function, effectively
decreasing the slope of the transfer function. The maximum
analog input signal range for which the gain coefficient can
compensate is 1.035 × V
0.965 × V
voltage.
CALIBRATING THE ADC
The ADuC814 has two hardware calibration modes, device
calibration and system calibration, that can be easily initiated by
the user software. The ADCCON3 SFR is used to calibrate the
ADC. See Table 8.
Device calibration is so called because the relevant signals used
for the calibration are available internally to the ADC. This
calibration method can be used to compensate for significant
changes in operating conditions, such as core frequency, analog
input range, reference voltage and supply voltages. In this
calibration mode, offset calibration uses internal AGND
selected via the ADCCON2 register bits CS3–CS0 (1011), and
gain calibration uses internal V
Offset calibration should be executed first, followed by gain
calibration.
System calibration is so called because the AGND and V
required for calibration must be the system AGND and V
signals. These must be supplied in turn, externally, to the ADC
inputs. This calibration method can be used to compensate for
both internal and external system errors. To perform system
calibration using an external reference, tie system ground and
reference to any two of the six selectable inputs. Enable external
reference mode (ADCCON1.6). Select the channel connected to
AGND via CS3–CS0 and perform system offset calibration.
Select the channel connected to V
system gain calibration.
INITIATING CALIBRATION IN CODE
When calibrating the ADC, ADCCON1 should be set to the
configuration in which the ADC is used. The ADCCON3
register can then be used to configure and execute the offset
and gain calibration required in sequence.
Configure the ADC as required. In this case, ADCCLK = /4,
acquisition time is set to 1 clock (T
MOV ADCCON1,#0D0H
REF
, which equates to typically ±3.5% of the reference
REF
, and the minimum input range is
;ADC on, ADCCLK set to
;divide by 4, 1 acquisition
;clock (Tacq)
REF
REF
selected by CS3–CS0 (1100).
ACQ
via CS3–CS0 and perform
), and ADC is enabled.
REF
REF
Rev. A | Page 29 of 72
To perform device offset calibration:
MOV ADCCON2,#0BH
MOV ADCCON3,#25H
To perform device gain calibration:
MOV ADCCON2,#0CH
ADCCON3,#27H
To perform system offset calibration:
Connect system AGND to an ADC input (Channel 0 in this case).
MOV ADCCON2,#00H
MOV ADCCON3,#25H
To perform system gain calibration:
Connect system V
MOV ADCCON2,#01H
ADCCON3,#27H
The calibration cycle time T
For an ADCCLK/F
NUMAV = 31, the calibration cycle time is
In a calibration cycle, the ADC busy flag (Bit 7), instead of
framing an individual ADC conversion as in normal mode, goes
high at the start of calibration and returns to zero only at the
end of the calibration cycle. It can therefore be monitored in
code to indicate when the calibration cycle is completed. The
following code can be used to monitor the BUSY signal during
a calibration cycle.
WAIT:
T
MOV A, ADCCON3
JB ACC.7, WAIT
CAL
T
CAL
= 14 × ADCCLK × NUMAV × (16 + T
= 14 × (1 / 4194304) × 31 × (16 + 1)
REF
CORE
to an ADC input (Channel 1 in this case).
, divide ratio of 4, a T
T
CAL
;select internal AGND
;select offset calibration,
;select internal V
;select offset calibration,
;select external AGND
;select offset calibration,
;select external V
;select offset calibration,
;31 averages per bit,
;offset calibration
;31 averages per bit,
;offset calibration
;31 averages per bit
;31 averages / bit (NUMAV),
;offset calibration
CAL
= 1.76 mS
is calculated by
;move ADCCON3 to A
;If bit 7 is set jump to
;else continue
WAIT
ACQ
= 1 ADCCLK,
ADuC814
REF
REF
ACQ
MOV
MOV
)