MC68HC08AZ32A Datasheet, PDF (121/312 Pages) Motorola, Inc – HCMOS Microcontroller Unit

Interrupts
11.5.1 MSCAN Extended ID Rejected if Stuff Bit Between ID16 and ID15
For 32-bit and 16-bit identifier acceptance modes, an extended ID CAN frame with a stuff bit between
ID16 and ID15 can be erroneously rejected, depending on IDAR0, IDAR1, and IDMR1.
Extended IDs (ID28–ID0) which generate a stuff bit between ID16 and ID15:
IDAR0
IDAR1
IDAR2
IDAR3
******** ***1111x xxxxxxxx xxxxxxxx
where: x = 0 or 1 (don't care)
* = pattern for ID28 to ID18 (see the following).
Affected extended IDs (ID28 - ID18) patterns:
a) xxxxxxxxx01 exceptions: 00000000001
xxxx1000001 exception: 11111000001
b) xxxxx100000 exception: 01111100000
c) xxxx0111111 exception: 00000111111
d) x0111110000
e) 10000000000
f) 11111111111
g) 10000011111
01111100001
When an affected ID is received, an incorrect value is compared to the 2nd byte of the filter (IDAR1 and
IDAR5, plus IDAR3 and IDAR7 in 16-bit mode). This incorrect value is the shift register contents before
ID15 is shifted in (i.e., right shifted by 1).
Workaround
If the problematic IDs cannot be avoided, the workaround is to mask certain bits with IDMR1 (and
IDMR5, plus IDMR3 and IDMR7 in 16-bit mode).
Example 1: to receive the message IDs
xxxx xxxx x011 111x xxxx xxxx xxxx xxxx
IDMR1 etc. must be 111x xxx1, i.e. ID20, 19, 18, 15 must be masked.
Example 2: to receive the message IDs
xxxx 0111 1111 111x xxxx xxxx xxxx xxxx
IDMR1 etc. must be 1xxx xxx1, i.e. ID20 and ID15 must be masked.
In general, using IDMR1 etc. 1111 xxx1, i.e. masking ID20, ID19, ID18, SRR, ID15, hides the
problem.
11.6 Interrupts
The MSCAN08 supports four interrupt vectors mapped onto eleven different interrupt sources, any of
which can be individually masked (for details see 11.13.5 MSCAN08 Receiver Flag Register (CRFLG) to
11.13.8 MSCAN08 Transmitter Control Register).
• Transmit Interrupt: At least one of the three transmit buffers is empty (not scheduled) and can be
loaded to schedule a message for transmission. The TXE flags of the empty message buffers are
set.
• Receive Interrupt: A message has been received successfully and loaded into the foreground
receive buffer. This interrupt will be emitted immediately after receiving the EOF symbol. The RXF
flag is set.
MC68HC08AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
121