Datasheet

Data Sheet ADuC7060/ADuC7061
Rev. D | Page 47 of 108
Bit Name Description
6:4 ADC1REF[2:0] Auxiliary channel ADC reference select.
[000] = internal reference selected. In ADC low power mode, the voltage reference selection is controlled by
ADCMODE[5].
[001] = external reference inputs (VREF+, VREF−) selected. Set the HIGHEXTREF1 bit if reference voltage
exceeds 1.3 V.
[010] = auxiliary external reference inputs (ADC4/EXT_REF2IN+, ADC5/EXT_REF2IN−) selected. Set the
HIGHEXTREF1 bit if reference voltage exceeds 1.35 V.
[011] = (AVDD, AGND) divide-by-2 selected. If this configuration is selected, the HIGHEXTREF1 bit is set
automatically.
[100] = (AVDD, ADC3). ADC3 can be used as the negative input terminal for the reference source.
[101] to [111] = reserved.
3:2 BUF_BYPASS[1:0] Buffer bypass.
[00] = full buffer on. Both positive and negative buffer inputs active.
[01] = negative buffer is bypassed, positive buffer is on.
[10] = negative buffer is on, positive buffer is bypassed.
[11] = full buffer bypass. Both positive and negative buffer inputs are off.
1:0 Digital gain. Select for auxiliary ADC inputs.
[00] = ADC1 gain = 1.
[01] = ADC1 gain = 2.
[10] = ADC1 gain = 4.
[11] = ADC1 gain = 8.
ADC Filter Register
Name: ADCFLT
Address: 0xFFFF0514
Default value: 0x0007
Access: Read and write
Function: The ADC filter MMR is a 16-bit register that controls the speed and resolution of both the on-chip ADCs. Note that, if
ADCFLT is modified, the primary and auxiliary ADCs are reset.
Table 45. ADCFLT MMR Bit Designations
Bit Name Description
15 CHOPEN Chop enable. Set by user to enable system chopping of all active ADCs. When this bit is set, the ADC has very low offset
errors and drift, but the ADC output rate is reduced by a factor of 3 if AF = 0 (see sinc3 decimation factor, Bits[6:0] in this
table). If AF > 0, then the ADC output update rate is the same with chop on or off. When chop is enabled, the settling time
is two output periods.
14 RAVG2 Running average-by-2 enable bit.
Set by user to enable a running-average-by-2 function, reducing ADC noise. This function is automatically enabled when
chopping is active. It is an optional feature when chopping is inactive, and if enabled (when chopping is inactive), does
not reduce the ADC output rate but does increase the settling time by one conversion period.
Cleared by user to disable the running average function.
13:8 AF[5:0] Averaging factor (AF). The values written to these bits are used to implement a programmable first-order sinc3 post filter.
The averaging factor can further reduce ADC noise at the expense of output rate as described in Bits[6:0] (sinc3
decimation factor) in this table.