Functional Description
SADC is a successive approximation register (SAR) based ADC. It can sample one of 8 analog sources at a given time, using an input mux. Two of the channels are used internally for VBAT and Temperature monitoring that can be used for adjusting the analog and RF circuitry configurations for optimum performance. SADC can be reconfigured to perform single-ended or differential measurements. The reference voltage can be internally generated or supplied as one of the external inputs. The internal reference voltage can be programmed as 0.85 V, 1.28 V and 1.6 V. For any specific reference value (Vref), the maximum ADC input is supposed to be (2 x Vref). Other aspects of Analog-to-Digital conversion can be controlled by programming SNSADC_CFG register.
SADC Operation
- Pairs of successive 13-bit samples from SADC are combined into 32-bit words by 16-bit aligning the samples. 32-bit words are stored into an SADC FIFO of 64 32-bit entries, where each entry would hold 2 samples.
- When the SADC FIFO entry count reaches the 6-bit threshold value specified in FIFO_THD register, the samples stored in the FIFO are automatically streamed to the SRAM by way of DMA Controller. (DMA Controller Channel 7 assigned to SADC must be programmed accordingly).
- The SADC FIFO status (not-empty signal and the entry count) can be polled in the FIFO_STAT register.
- The SADC FIFO can also be “popped” by one entry, by reading the FIFO_RD register.
SADC Sample Operation Mode
SADC supports two sample operation modes: single-end measurement mode and differential measurement mode. You can choose the mode by programming MODE bit of CFG reg.
- In single-end measurement mode, the input signal should be assigned to channel N. In differential measurement mode, the input signals should be assigned to channel P and channel N. You can make the assignment by programming CH_P bit and CH_N bit of CFG register.
- In single-end measurement mode, the output is the measurement of voltage between CH_N to GND. The maximum is 2*Vref, and the minimum is 0 V. In differential measurement mode, the output is the measurement of difference voltage between CH_P to CH_N.The maximum is 2*Vref, and the minimum is -2*Vref.
