Reference Selection And Input Range Definition - Silicon Laboratories EFR32xG14 Wireless Gecko Reference Manual

Reference Manual
ADC - Analog to Digital Converter
26.3.7.3 APORT Conflicts
The ADC shares common analog buses connected to its APORTs (1-4) with other analog peripherals (see device-specific data sheet).
As the ADC performs single or scan conversions, it requests the shared buses and sends selections for the control switches to connect
the desired I/O pins. If another analog peripheral requests the same shared bus at the same time, there will be a collision and none of
the peripherals will be granted control of that bus.
To help debug over-utilization of APORT resources, the ADC hardware provides status information in local registers. The ADCn_APOR-
TREQ register gives the user visibility into which APORT(s) the ADC is requesting given the setting of the input selection registers.
ADCn_APORTCONFLICT reports any conflicts that occur. If PROGERR in ADCn_IEN is set, any conflict generates an interrupt. The
PROGERR field in the ADCn_STATUS register indicates whether the programming error happened as a result of an APORT bus con-
flict (BUSCONF) or from a negative-input selection conflict (NEGSELCONF). If the PROGERR interrupt occurred due to a negative se-
lection conflict, then the interrupt can be cleared by software only after correcting the conflict. If a software clear is attempted without
correcting the configuration, the interrupt will be cleared for one clock cycle but then it will trigger again as the invalid configuration still
persists.
Note: The ADC requests shared bus connections as soon as that bus is selected in the input select registers, even if the ADC is not
performing any conversions. This means that by using the APORT request, the ADC will acquire the associated shared analog bus,
preventing other peripherals from using it. The bus will be released only when the input select registers are changed.
It is possible for the ADC to passively monitor shared bus signals without controlling the switches and creating bus conflicts. This can
be done by setting the ADCn_APORTMASTERDIS register. When ADCn_APORTMASTERDIS is used, channel selection defers to the
peripheral acting as the bus master for that shared bus, and no bus conflict will occur. The ADC will connect its input to the shared bus,
but the specific channel will be controlled by the peripheral designated as the bus master.

26.3.8 Reference Selection and Input Range Definition

The full scale voltage (VFS) of the ADC is defined as the full input range, from the lowest possible input voltage to the highest. For
single-ended conversions, the input range on the selected positive input is from 0 to VFS. For differential conversions, the input to the
converter is the difference between the positive and negative input selections. This can range from -VFS/2 to +VFS/2.
VFS for the converter is determined by a combination of the selected voltage reference (VREF) and programmable divider circuits on
the ADC input and voltage reference paths. Users have full control over the VREF and divider selections, offering a very flexible and
wide selection of VFS values. In most applications however, it is not necessary to adjust VFS beyond a set of common pre-defined
choices. For the simplest VFS configuration, refer to 26.3.8.1 Basic Full-Scale Voltage Configuration. If the application requires a VFS
configuration not available in the pre-defined choices, 26.3.8.2 Advanced Full-Scale Voltage Configuration covers additional configura-
tion options.
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