Table 584. Cu Interrupt Enable Register Field Descriptions - STMicroelectronics SPC572L series Reference Manual

CAN Subsystem

Table 584. CU Interrupt Enable Register field descriptions

Field
Calibration State Changed Enable
30
0 Interrupt disabled
CSCE
1 Interrupt enabled
Calibration Watchdog Event Enable
31
0 Interrupt disabled
CWEE
1 Interrupt enabled
44.3.16.4 Functional Description
Calibration of the time quanta clock cu_tcq via CAN messages is performed by adapting a
clock divider that generates the CAN protocol time quantum tq from the clock cu_pclk.
•
First step: Basic Calibration–The minimum distance between two edges from recessive
to dominant is measured, this time to be assumed two CAN bit times, counted in PLL
clock periods. The clock divider is updated each time a new measurement finds a
smaller distance between edges. Basic calibration is achieved when the CAN protocol
controller detects a valid CAN message. This is signaled to the Calibration on CAN unit
by input signal cu_mrx.
•
Second step: Precision Calibration – The calibration state machine measures the
length of a longer bit sequence inside a CAN frame by counting the number of cu_pclk
periods. The length of this bit sequence can be configured to 32 or 64 bits via
CCFG.CLF. For a calibration field length of 32/64 bit a calibration message with at least
2/6 byte data field is required. The counter is controlled by input signals cu_calf and
cu_spt. The counter is enabled when cu_calf is set and stops after the configured
number of bits has been received. Received bits are signaled by the M_CAN by signal
cu_spt. Precision calibration is based on the new clock divider value calculated from
the measurement of the longer bit sequence.
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Description
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