Production Data
WM8321
18 AUXILIARY ADC
18.1 GENERAL DESCRIPTION
The WM8321 incorporates a 12-bit Auxiliary ADC (AUXADC). This can be used to perform a number
of system measurements (including supply voltages and battery temperature) and can also be used to
measure analogue voltages from external sources and sensors.
External inputs to the AUXADC should be connected to the pins GPIO10, GPIO11 and GPIO12. The
maximum voltage that can be measured is determined by the power domain associated with each;
this is selectable on a pin by pin basis as described in Section 21.3.
Note that, when GPIO10, GPIO11 or GPIO12 is used as an input to the AUXADC, then the normal
GPIO functionality cannot be supported on the affected pin(s). In this case, it is recommended that
the respective GPIO(s) are tri-stated, as described in Section 21.3.
18.2 AUXADC CONTROL
The AUXADC is enabled by setting the AUX_ENA register bit. By default, the AUXADC is not enabled
in the SLEEP state, but this can be selected using the AUX_SLPENA field.
The AUXADC measurements can be initiated manually or automatically. For automatic operation, the
AUX_RATE register is set according to the required conversion rate, and conversions are enabled by
setting the AUX_CVT_ENA bit. For manual operation, the AUX_RATE register is set to 00h, and each
manual conversion is initiated by setting the AUX_CVT_ENA bit. In manual mode, the
AUX_CVT_ENA bit is reset by the WM8321 after each conversion. (Note that the conversion result is
not available for readback until the AUXADC interrupt is asserted, as described in Section 18.5.)
The AUXADC has 5 available input sources. Each of these inputs is enabled by setting the respective
bit in the AuxADC Source Register (R16431).
For each AUXADC measurement event (in Manual or Automatic modes), the WM8321 selects the
next enabled input source. Any number of inputs may be selected simultaneously; the AUXADC will
measure each one in turn. Note that only a single AUXADC measurement is made on any Manual or
Automatic trigger.
For example, if the GPIO10, GPIO12 and PVDD voltages are enabled for AUXADC measurement,
then GPIO10 would be measured in the first instance, and GPIO12 then PVDD would be measured
on the next manual or automatic AUXADC triggers. In this case, a total of three manual or automatic
AUXADC triggers would be required to measure all of the selected inputs.
The control fields associated with initiating AUXADC measurements are defined in Table 45.
ADDRESS
R16430
BIT
LABEL
AUX_ENA
DEFAULT
DESCRIPTION
AUXADC Enable
15
0
(402Eh)
0 = Disabled
1 = Enabled
AuxADC
Control
Note - this bit is reset to 0 when the
OFF power state is entered.
AUX_CVT_ENA
AUXADC Conversion Enable
0 = Disabled
14
0
1 = Enabled
In automatic mode, conversions are
enabled by setting this bit.
In manual mode (AUX_RATE = 0),
setting this bit will initiate a
conversion; the bit is reset
automatically after each conversion.
AUX_SLPENA
AUXADC SLEEP Enable
0 = Disabled
12
0
1 = Controlled by AUX_ENA
PD, February 2012, Rev 4.0
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
