Figure 538. Calibration Fsm - STMicroelectronics SPC572L series Reference Manual

RM0400
T5
Precision_Calibrated
T0: HW reset
T1: check for minimum
T2: message received (cu_mrx = '1')
T3: evaluate messages
T4: quartz message received (cu_qmrx = '1')
T5: evaluate quartz messages
T6: configuration change enabled (cu_cce = '1')
T7: watchdog event: no quartz message received
T8: watchdog event: no message received
A change of the calibration state is signaled via by output cu_csc. The duration of a cu_csc
pulse is one cu_hclk period.
A change of the calibration state also sets interrupt flag cuir.csc. If enabled by cuie.csce,
interrupt line cu_int is activated (set to high). Interrupt line cu_int remains active until
interrupt flag cuir.csc is reset.
Until precision calibration is achieved (cu_cok='1'), the attached M_CANs operate in a
restricted mode (no frame transmission, no error or overload flag transmission, no error
counting). In case calibration of the PLL is done by software by evaluating the calibration
status from register CSTAT, the attached M_CANs have to be set to restricted operation
mode (CCCR.ASM = '1') until the Calibration on CAN unit is in state Precision_Calibrated
(see Section 44.3.16.4.3: Software
Precision calibration may be performed only on valid CAN frames transmitted by a node
with a stable, quartz-controlled clock. Calibration frames are detected by the M_CAN's
acceptance filtering and are signaled to the Clock Calibration on CAN unit by signal
cu_qmrx. A filter element and an Rx Buffer have to be configured in the attached M_CAN to
identify and store calibration messages. After reception of a calibration message the Rx
Buffer's new data flag has to be reset to enable signaling of the next calibration message.
In case there is only one CAN transmitter with a quartz clock in the network, this node has to
transmit its first message after startup with at least one "1010" sequence in the data field or
in the identifier. This assures that the non-quartz nodes can enter state Basic_Calibrated
and then acknowledge the quartz node's messages.

Figure 538. Calibration FSM

HW reset
T6
CALS = 10
or configuration change enabled (cu_cce = '1')
DocID027809 Rev 4
T0
T1
Not_Calibrated
CALS = 00
T2
T4
T7
Calibration).
CAN Subsystem
T8
T3
Basic_Calibrated
CALS = 01
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