PIC18F2585_07 Datasheet, PDF (341/482 Pages) Microchip Technology – Enhanced Flash Microcontrollers with ECAN Technology, 10-Bit A/D and nanoWatt Technology

PIC18F2585/2680/4585/4680
The PIC18F2585/2680/4585/4680 devices are error-
active if both error counters are below the error-passive
limit of 128. They are error-passive if at least one of the
error counters equals or exceeds 128. They go to bus-
off if the transmit error counter equals or exceeds the
bus-off limit of 256. The devices remain in this state
until the bus-off recovery sequence is received. The
bus-off recovery sequence consists of 128 occurrences
of 11 consecutive recessive bits (see Figure 23-8).
Note that the CAN module, after going bus-off, will
recover back to error-active without any intervention by
the MCU if the bus remains Idle for 128 x 11 bit times.
If this is not desired, the error Interrupt Service Routine
should address this. The current Error mode of the
CAN module can be read by the MCU via the
COMSTAT register.
Additionally, there is an Error State Warning flag bit,
EWARN, which is set if at least one of the error
counters equals or exceeds the error warning limit of
96. EWARN is reset if both error counters are less than
the error warning limit.
FIGURE 23-8:
ERROR MODES STATE DIAGRAM
Reset
RXERRCNT < 127 or
TXERRCNT < 127
Error-
Active
Error-
Passive
RXERRCNT > 127 or
TXERRCNT > 127
TXERRCNT > 255
Bus-
Off
128 occurrences of
11 consecutive
“recessive” bits
23.15 CAN Interrupts
The module has several sources of interrupts. Each of
these interrupts can be individually enabled or
disabled. The PIR3 register contains interrupt flags.
The PIE3 register contains the enables for the 8 main
interrupts. A special set of read-only bits in the
CANSTAT register, the ICODE bits, can be used in
combination with a jump table for efficient handling of
interrupts.
All interrupts have one source, with the exception of the
error interrupt and buffer interrupts in Mode 1 and 2. Any
of the error interrupt sources can set the error interrupt
flag. The source of the error interrupt can be determined
by reading the Communication Status register,
COMSTAT. In Mode 1 and 2, there are two interrupt
enable/disable and flag bits – one for all transmit buffers
and the other for all receive buffers.
The interrupts can be broken up into two categories:
receive and transmit interrupts.
The receive related interrupts are:
• Receive Interrupts
• Wake-up Interrupt
• Receiver Overrun Interrupt
• Receiver Warning Interrupt
• Receiver Error-Passive Interrupt
The transmit related interrupts are:
• Transmit Interrupts
• Transmitter Warning Interrupt
• Transmitter Error-Passive Interrupt
• Bus-Off Interrupt
© 2007 Microchip Technology Inc.
Preliminary
DS39625C-page 339