Datasheet

PIC18F2480/2580/4480/4580
DS39637D-page 346 © 2009 Microchip Technology Inc.
24.15.1 INTERRUPT CODE BITS
To simplify the interrupt handling process in user firm-
ware, the ECAN module encodes a special set of bits. In
Mode 0, these bits are ICODE<3:1> in the CANSTAT
register. In Mode 1 and 2, these bits are EICODE<4:0> in
the CANSTAT register. Interrupts are internally prioritized
such that the higher priority interrupts are assigned lower
values. Once the highest priority interrupt condition has
been cleared, the code for the next highest priority inter-
rupt that is pending (if any) will be reflected by the ICODE
bits (see Table 24-5). Note that only those interrupt
sources that have their associated interrupt enable bit set
will be reflected in the ICODE bits.
In Mode 2, when a receive message interrupt occurs,
the EICODE bits will always consist of ‘10000’. User
firmware may use FIFO Pointer bits to actually access
the next available buffer.
24.15.2 TRANSMIT INTERRUPT
When the transmit interrupt is enabled, an interrupt will
be generated when the associated transmit buffer
becomes empty and is ready to be loaded with a new
message. In Mode 0, there are separate interrupt enable/
disable and flag bits for each of the three dedicated trans-
mit buffers. The TXBnIF bit will be set to indicate the
source of the interrupt. The interrupt is cleared by the
MCU, resetting the TXBnIF bit to a ‘0’. In Mode 1 and 2,
all transmit buffers share one interrupt enable/disable bit
and one flag bit. In Mode 1 and 2, TXBIE in PIE3 and
TXBIF in PIR3 indicate when a transmit buffer has com-
pleted transmission of its message. TXBnIF, TXBnIE and
TXBnIP in PIR3, PIE3 and IPR3, respectively, are not
used in Mode 1 and 2. Individual transmit buffer interrupts
can be enabled or disabled by setting or clearing TXBIE
and B0IE register bits. When a shared interrupt occurs,
user firmware must poll the TXREQ bit of all transmit
buffers to detect the source of interrupt.
24.15.3 RECEIVE INTERRUPT
When the receive interrupt is enabled, an interrupt will
be generated when a message has been successfully
received and loaded into the associated receive buffer.
This interrupt is activated immediately after receiving
the End-Of-Frame (EOF) field.
In Mode 0, the RXBnIF bit is set to indicate the source
of the interrupt. The interrupt is cleared by the MCU,
resetting the RXBnIF bit to a ‘0’.
In Mode 1 and 2, all receive buffers share RXBIE,
RXBIF and RXBIP in PIE3, PIR3 and IPR3, respec-
tively. Bits, RXBnIE, RXBnIF and RXBnIP, are not
used. Individual receive buffer interrupts can be con-
trolled by the TXBIE and BIE0 registers. In Mode 1,
when a shared receive interrupt occurs, user firmware
must poll the RXFUL bit of each receive buffer to detect
the source of interrupt. In Mode 2, a receive interrupt
indicates that the new message is loaded into FIFO.
FIFO can be read by using FIFO Pointer bits, FP.
TABLE 24-5: VALUES FOR ICODE<2:0>
24.15.4 MESSAGE ERROR INTERRUPT
When an error occurs during transmission or reception
of a message, the message error flag, IRXIF, will be set
and if the IRXIE bit is set, an interrupt will be generated.
This is intended to be used to facilitate baud rate
determination when used in conjunction with Listen
Only mode.
24.15.5 BUS ACTIVITY WAKE-UP
INTERRUPT
When the PIC18F2480/2580/4480/4580 devices are in
Sleep mode and the bus activity wake-up interrupt is
enabled, an interrupt will be generated and the WAKIF
bit will be set when activity is detected on the CAN bus.
This interrupt causes the PIC18F2480/2580/4480/
4580 devices to exit Sleep mode. The interrupt is reset
by the MCU, clearing the WAKIF bit.
24.15.6 ERROR INTERRUPT
When the CAN module error interrupt (ERRIE in PIE3)
is enabled, an interrupt is generated if an overflow con-
dition occurs, or if the error state of the transmitter or
receiver has changed. The error flags in COMSTAT will
indicate one of the following conditions.
ICODE
<2:0>
Interrupt Boolean Expression
000 None ERR
•WAK•TX0•TX1•TX2•RX0•RX1
001 Error ERR
010 TXB2 ERR•TX0•TX1•TX2
011 TXB1 ERR•TX0•TX1
100 TXB0 ERR•TX0
101 RXB1 ERR•TX0•TX1•TX2•RX0•RX1
110 RXB0 ERR•TX0•TX1•TX2•RX0
111
Wake on
Interrupt
ERR
•TX0•TX1•TX2•RX0•RX1•WAK
Legend:
ERR = ERRIF * ERRIE RX0 = RXB0IF * RXB0IE
TX0 = TXB0IF * TXB0IE RX1 = RXB1IF * RXB1IE
TX1 = TXB1IF * TXB1IE WAK = WAKIF * WAKIE
TX2 = TXB2IF * TXB2IE