DocID024597 Rev 5 279/1830
RM0351 Clock recovery system (CRS) (only valid for STM32L496xx/4A6xx devices)
289
7 Clock recovery system (CRS) (only valid for
STM32L496xx/4A6xx devices)
7.1 Introduction
The clock recovery system (CRS) is an advanced digital controller acting on the internal
fine-granularity trimmable RC oscillator HSI48. The CRS provides a powerful means for
oscillator output frequency evaluation, based on comparison with a selectable
synchronization signal. It is capable of doing automatic adjustment of oscillator trimming
based on the measured frequency error value, while keeping the possibility of a manual
trimming.
The CRS is ideally suited to provide a precise clock to the USB peripheral. In such case, the
synchronization signal can be derived from the start-of-frame (SOF) packet signalization on
the USB bus, which is sent by a USB host at precise 1-ms intervals.
The synchronization signal can also be derived from the LSE oscillator output or it can be
generated by user software.
7.2 CRS main features
• Selectable synchronization source with programmable prescaler and polarity:
– External pin
– LSE oscillator output
– USB SOF packet reception
• Possibility to generate synchronization pulses by software
• Automatic oscillator trimming capability with no need of CPU action
• Manual control option for faster start-up convergence
• 16-bit frequency error counter with automatic error value capture and reload
• Programmable limit for automatic frequency error value evaluation and status reporting
• Maskable interrupts/events:
– Expected synchronization (ESYNC)
– Synchronization OK (SYNCOK)
– Synchronization warning (SYNCWARN)
– Synchronization or trimming error (ERR)
To Next Page
Loading...
Need help?
General
