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Chapter 22 FlexCAN
MPC5602P Microcontroller Reference Manual, Rev. 4
554
Freescale Semiconductor
22.3.4.7
Error Counter Register (ECR)
This register has two 8-bit fields that reflect the value of two FlexCAN error counters:
•
Transmit Error Counter (Tx_Err_Counter field)
•
Receive Error Counter (Rx_Err_Counter field)
The rules for increasing and decreasing these counters are described in the CAN protocol and are
completely implemented in the FlexCAN module. Both counters are read only except in Test Mode or
Freeze Mode, where they can be written by the CPU.
Writing to the Error Counter Register while in Freeze Mode is an indirect operation. The data is first
written to an auxiliary register and then an internal request/acknowledge procedure across clock domains
is executed. All this is transparent to the user, except for the fact that the data will take some time to be
actually written to the register. If desired, software can poll the register to discover when the data was
actually written.
FlexCAN responds to any bus state as described in the protocol, e.g., transmit ‘Error Active’ or ‘Error
Passive’ flag, delay its transmission start time (‘Error Passive’) and avoid any influence on the bus when
in ‘Bus Off’ state. The following are the basic rules for FlexCAN bus state transitions.
•
If the value of Tx_Err_Counter or Rx_Err_Counter increases to be greater than or equal to 128, the
FLT_CONF field in the Error and Status Register is updated to reflect ‘Error Passive’ state.
•
If the FlexCAN state is ‘Error Passive’, and either Tx_Err_Counter or Rx_Err_Counter decrements
to a value less than or equal to 127 while the other already satisfies this condition, the FLT_CONF
field in the Error and Status Register is updated to reflect ‘Error Active’ state.
•
If the value of Tx_Err_Counter increases to be greater than 255, the FLT_CONF field in the Error
and Status Register is updated to reflect ‘Bus Off’ state, and an interrupt may be issued. The value
of Tx_Err_Counter is then reset to 0.
•
If FlexCAN is in ‘Bus Off’ state, then Tx_Err_Counter is cascaded together with another internal
counter to count the 128th occurrences of 11 consecutive recessive bits on the bus. Hence,
Tx_Err_Counter is reset to 0 and counts in a manner where the internal counter counts 11 such bits
and then wraps around while incrementing the Tx_Err_Counter. When Tx_Err_Counter reaches
the value of 128, the FLT_CONF field in the Error and Status Register is updated to be ‘Error
Active’ and both error counters are reset to zero. At any instance of dominant bit following a stream
of less than 11 consecutive recessive bits, the internal counter resets itself to zero without affecting
the Tx_Err_Counter value.
•
If during system start-up, only one node is operating, then its Tx_Err_Counter increases in each
message it is trying to transmit, as a result of acknowledge errors (indicated by the ACK_ERR bit
Table 22-17. RX15MASK field description
Field
Description
0–31
MI31–MI0
Mask Bits
For normal Rx MBs, the mask bits affect the ID filter programmed on the MB. For the Rx FIFO, the mask bits
affect all bits programmed in the filter table (ID, IDE, RTR).
0 The corresponding bit in the filter is “don’t care.”
1 The corresponding bit in the filter is checked against the one received.
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Страница 4: ...MPC5602P Microcontroller Reference Manual Rev 4 4 Freescale Semiconductor ...
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Страница 380: ...Chapter 17 Flash Memory MPC5602P Microcontroller Reference Manual Rev 4 380 Freescale Semiconductor ...
Страница 532: ...Chapter 21 LIN Controller LINFlex MPC5602P Microcontroller Reference Manual Rev 4 532 Freescale Semiconductor ...
Страница 578: ...Chapter 22 FlexCAN MPC5602P Microcontroller Reference Manual Rev 4 578 Freescale Semiconductor ...
Страница 708: ...Chapter 25 FlexPWM MPC5602P Microcontroller Reference Manual Rev 4 708 Freescale Semiconductor ...
Страница 742: ...Chapter 26 eTimer MPC5602P Microcontroller Reference Manual Rev 4 742 Freescale Semiconductor ...
Страница 760: ...Chapter 27 Functional Safety MPC5602P Microcontroller Reference Manual Rev 4 760 Freescale Semiconductor ...
Страница 782: ...Chapter 28 Fault Collection Unit FCU MPC5602P Microcontroller Reference Manual Rev 4 782 Freescale Semiconductor ...
Страница 788: ...Chapter 29 Wakeup Unit WKPU MPC5602P Microcontroller Reference Manual Rev 4 788 Freescale Semiconductor ...
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