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ST150M User Manual
Confidential & Proprietary Information
9150-0125-01 R-1
Listed here are the main features for PDM:
• Up to two PDM microphones configured as a Left/Right pair using the same data input
• 16 kHz output sample rate, 16-bit samples
• EasyDMA support for sample buffering
• HW decimation filters
• Selectable ratio of 64 or 80 between PDM_CLK and output sample rate
4.2.4 PPI - PROGRAMMABLE PERIPHERAL INTERCONNECT
The programmable peripheral interconnect (PPI) enables peripherals to interact autonomously with each other using tasks
and events independent of the CPU. The PPI allows precise synchronization between peripherals when real-time application
constraints exist and eliminates the need for CPU activity to implement behavior which can be predefined using PPI.
On each PPI channel, the signals are synchronized to the 16 MHz clock, to avoid any internal violation of setup and hold
timings. As a consequence, events that are synchronous to the 16 MHz clock will be delayed by one clock period, while other
asynchronous events will be delayed by up to one 16 MHz clock period. Note that shortcuts (as defined in the SHORTS register
in each peripheral) are not affected by this 16 MHz synchronization, and are therefore not delayed.
4.2.5 PWM - PULSE WIDTH MODULATION
The pulse with modulation (PWM) module enables the generation of pulse width modulated signals on GPIO. The module
implements an up or up-and-down counter with four PWM channels that drive assigned GPIOs.
The following are the main features of a PWM module:
• Programmable PWM frequency
• Up to four PWM channels with individual polarity and duty cycle values
• Edge or center-aligned pulses across PWM channels
• Multiple duty cycle arrays (sequences) defined in RAM
• Autonomous and glitch-free update of duty cycle values directly from memory through EasyDMA (no CPU involvement)
• Change of polarity, duty cycle, and base frequency possibly on every PWM period
• RAM sequences can be repeated or connected into loops
4.2.6 QDEC - QUADRATURE DECODER
The Quadrature decoder (QDEC) provides buffered decoding of quadrature-encoded sensor signals. It is suitable for
mechanical and optical sensors.
The sample period and accumulation are configurable to match application requirements. The QDEC provides the following:
• Decoding of digital waveform from off-chip quadrature encoder.
• Sample accumulation eliminating hard real-time requirements to be enforced on application.
• Optional input de-bounce filters.
• Optional LED output signal for optical encoders.
The QDEC decodes the output from an incremental motion encoder by sampling the QDEC phase input pins (A and B). The
off-chip quadrature encoder is an incremental motion encoder outputting two waveforms, phase A and phase B. The two
output waveforms are always 90 degrees out of phase, meaning that one always changes level before the other. The direction of
movement is indicated by which of these two waveforms that changes level first.
Invalid transitions may occur, that is when the two waveforms switch simultaneously. This may occur if the wheel rotates too
fast relative to the sample rate set for the decoder. The QDEC decodes the output from the off-chip encoder by sampling the
QDEC phase input pins (A and B) at a fixed rate as specified in the SAMPLEPER register. If the SAMPLEPER value needs to be
changed, the QDEC shall be stopped using the STOP task.
