
Controller Area Network (FlexCAN)
PXN20 Microcontroller Reference Manual, Rev. 1
29-34
Freescale Semiconductor
then. If the MB is not unlocked in time and yet another new message with the same ID arrives, then the
new message overwrites the one on the SMB and there is no indication of lost messages either in the code
field of the MB or in the error and status register.
While the message is being moved-in from the SMB to the MB, the BUSY bit on the code field is asserted.
If the CPU reads the control and status word and finds out that the BUSY bit is set, it should defer accessing
the MB until the BUSY bit is negated.
NOTE
If the BUSY bit is asserted or if the MB is empty, then reading the control
and status word does not lock the MB.
Deactivation takes precedence over locking. If the CPU deactivates a locked Rx MB, then its lock status
is negated and the MB is marked as invalid for the current matching round. Any pending message on the
SMB is not transferred anymore to the MB.
29.4.6
Rx FIFO
The receive-only FIFO is enabled by asserting the FEN bit in the CAN
x
_MCR. The reset value of this bit
is zero to maintain software backwards compatibility with previous versions of the module that did not
have the FIFO feature. When the FIFO is enabled, the memory region normally occupied by the first 8
MBs (0x80-0xFF) is now reserved for use of the FIFO engine (see
Section 29.3.3, Rx FIFO Structure
Management of read and write pointers is done internally by the FIFO engine. The CPU can read the
received frames sequentially, in the order they were received, by repeatedly accessing a Message Buffer
structure at the beginning of the memory.
The FIFO can store as many as six frames pending service by the CPU. An interrupt is sent to the CPU
when new frames are available in the FIFO. Upon receiving the interrupt, the CPU must read the frame
(accessing an MB in the 0x80 address) and then clear the interrupt. The act of clearing the interrupt triggers
the FIFO engine to replace the MB in 0x80 with the next frame in the queue, and then issue another
interrupt to the CPU. If the FIFO is full and more frames continue to be received, an OVERFLOW
interrupt is issued to the CPU and subsequent frames are not accepted until the CPU creates space in the
FIFO by reading one or more frames. A warning interrupt is also generated when 4 frames are accumulated
in the FIFO.
A powerful filtering scheme is provided to accept only frames intended for the target application, thus
reducing the interrupt servicing work load. The filtering criteria is specified by programming a table of 8
32-bit registers that can be configured to one of the following formats (see also
•
Format A: 8 extended or standard IDs (including IDE and RTR)
•
Format B: 16 standard IDs or 16 extended 14-bit ID slices (including IDE and RTR)
•
Format C: 32 standard or extended 8-bit ID slices
NOTE
A chosen format is applied to all eight registers of the filter table. It is not
possible to mix formats within the table.
Содержание PXN2020
Страница 1: ...PXN20 Microcontroller Reference Manual Devices Supported PXN2020 PXN2120 PXN20RM Rev 1 06 2011...
Страница 42: ...PXN20 Microcontroller Reference Manual Rev 1 lxiv Freescale Semiconductor...
Страница 64: ...Introduction PXN20 Microcontroller Reference Manual Rev 1 1 22 Freescale Semiconductor...
Страница 112: ...Signal Description PXN20 Microcontroller Reference Manual Rev 1 3 44 Freescale Semiconductor...
Страница 118: ...Resets PXN20 Microcontroller Reference Manual Rev 1 4 6 Freescale Semiconductor...
Страница 162: ...Clocks Reset and Power CRP PXN20 Microcontroller Reference Manual Rev 1 6 30 Freescale Semiconductor...
Страница 182: ...Frequency Modulated Phase Locked Loop FMPLL PXN20 Microcontroller Reference Manual Rev 1 7 20 Freescale Semiconductor...
Страница 268: ...Boot Assist Module BAM PXN20 Microcontroller Reference Manual Rev 1 9 14 Freescale Semiconductor...
Страница 318: ...Interrupts and Interrupt Controller INTC PXN20 Microcontroller Reference Manual Rev 1 10 50 Freescale Semiconductor...
Страница 326: ...General Purpose Static RAM SRAM PXN20 Microcontroller Reference Manual Rev 1 11 8 Freescale Semiconductor...
Страница 372: ...e200z6 Core Z6 PXN20 Microcontroller Reference Manual Rev 1 13 8 Freescale Semiconductor...
Страница 412: ...e200z0 Core Z0 PXN20 Microcontroller Reference Manual Rev 1 14 14 Freescale Semiconductor...
Страница 460: ...Memory Protection Unit MPU PXN20 Microcontroller Reference Manual Rev 1 18 20 Freescale Semiconductor...
Страница 478: ...Error Correction Status Module ECSM PXN20 Microcontroller Reference Manual Rev 1 19 18 Freescale Semiconductor...
Страница 488: ...Software Watchdog Timer SWT PXN20 Microcontroller Reference Manual Rev 1 20 10 Freescale Semiconductor...
Страница 494: ...System Timer Module STM PXN20 Microcontroller Reference Manual Rev 1 21 6 Freescale Semiconductor...
Страница 821: ...Media Local Bus MLB PXN20 Microcontroller Reference Manual Rev 1 Freescale Semiconductor 27 49...
Страница 822: ...Media Local Bus MLB PXN20 Microcontroller Reference Manual Rev 1 27 50 Freescale Semiconductor...
Страница 926: ...Controller Area Network FlexCAN PXN20 Microcontroller Reference Manual Rev 1 29 42 Freescale Semiconductor...
Страница 990: ...Deserial Serial Peripheral Interface DSPI PXN20 Microcontroller Reference Manual Rev 1 30 64 Freescale Semiconductor...
Страница 1044: ...Enhanced Serial Communication Interface eSCI PXN20 Microcontroller Reference Manual Rev 1 31 54 Freescale Semiconductor...
Страница 1080: ...Cross Triggering Unit CTU PXN20 Microcontroller Reference Manual Rev 1 33 12 Freescale Semiconductor...
Страница 1134: ...Analog to Digital Converter ADC PXN20 Microcontroller Reference Manual Rev 1 34 54 Freescale Semiconductor...
Страница 1150: ...IEEE 1149 1 Test Access Port Controller JTAGC PXN20 Microcontroller Reference Manual Rev 1 35 16 Freescale Semiconductor...
Страница 1257: ...Nexus Development Interface NDI PXN20 Microcontroller Reference Manual Rev 1 Freescale Semiconductor 36 107...
Страница 1258: ...Nexus Development Interface NDI PXN20 Microcontroller Reference Manual Rev 1 36 108 Freescale Semiconductor...
Страница 1376: ...Memory Map PXN20 Microcontroller Reference Manual Rev 1 A 118 Freescale Semiconductor...