Microchip Technology MA300015 Data Sheet
© 2011 Microchip Technology Inc.
DS70150E-page 131
dsPIC30F6010A/6015
• Receive Error Interrupts
A receive error interrupt will be indicated by the ERRIF
bit. This bit shows that an error condition occurred. The
source of the error can be determined by checking the
bits in the CAN Interrupt STATUS register, CiINTF.
bit. This bit shows that an error condition occurred. The
source of the error can be determined by checking the
bits in the CAN Interrupt STATUS register, CiINTF.
• Invalid message received
If any type of error occurred during reception of the last
message, an error will be indicated by the IVRIF bit.
message, an error will be indicated by the IVRIF bit.
• Receiver overrun
The RXnOVR bit indicates that an overrun condition
occurred.
occurred.
• Receiver warning
The RXWAR bit indicates that the Receive Error Coun-
ter (RERRCNT<7:0>) has reached the Warning limit of
96.
ter (RERRCNT<7:0>) has reached the Warning limit of
96.
• Receiver error passive
The RXEP bit indicates that the Receive Error Counter
has exceeded the Error Passive limit of 127 and the
module has gone into Error Passive state.
has exceeded the Error Passive limit of 127 and the
module has gone into Error Passive state.
19.5
Message Transmission
19.5.1
TRANSMIT BUFFERS
The CAN module has three transmit buffers. Each of
the three buffers occupies 14 bytes of data. Eight of the
bytes are the maximum 8 bytes of the transmitted mes-
sage. Five bytes hold the standard and extended
identifiers and other message arbitration information.
the three buffers occupies 14 bytes of data. Eight of the
bytes are the maximum 8 bytes of the transmitted mes-
sage. Five bytes hold the standard and extended
identifiers and other message arbitration information.
19.5.2
TRANSMIT MESSAGE PRIORITY
Transmit priority is a prioritization within each node of the
pending transmittable messages. There are 4 levels of
transmit priority. If TXPRI<1:0> (CiTXnCON<1:0>, where
n = 0, 1 or 2 represents a particular transmit buffer) for a
particular message buffer is set to ‘11’, that buffer has the
highest priority. If TXPRI<1:0> for a particular message
buffer is set to ‘10’ or ‘01’, that buffer has an intermediate
priority. If TXPRI<1:0> for a particular message buffer is
‘00’, that buffer has the lowest priority.
pending transmittable messages. There are 4 levels of
transmit priority. If TXPRI<1:0> (CiTXnCON<1:0>, where
n = 0, 1 or 2 represents a particular transmit buffer) for a
particular message buffer is set to ‘11’, that buffer has the
highest priority. If TXPRI<1:0> for a particular message
buffer is set to ‘10’ or ‘01’, that buffer has an intermediate
priority. If TXPRI<1:0> for a particular message buffer is
‘00’, that buffer has the lowest priority.
19.5.3
TRANSMISSION SEQUENCE
To initiate transmission of the message, the TXREQ bit
(CiTXnCON<3>) must be set. The CAN bus module
resolves any timing conflicts between setting of the
TXREQ bit and the Start of Frame (SOF), ensuring
that if the priority was changed, it is resolved correctly
before the SOF occurs. When TXREQ is set, the
TXABT (CiTXnCON<6>), TXLARB (CiTXnCON<5>)
and TXERR (CiTXnCON<4>) flag bits are
automatically cleared.
(CiTXnCON<3>) must be set. The CAN bus module
resolves any timing conflicts between setting of the
TXREQ bit and the Start of Frame (SOF), ensuring
that if the priority was changed, it is resolved correctly
before the SOF occurs. When TXREQ is set, the
TXABT (CiTXnCON<6>), TXLARB (CiTXnCON<5>)
and TXERR (CiTXnCON<4>) flag bits are
automatically cleared.
Setting TXREQ bit simply flags a message buffer as
enqueued for transmission. When the module detects
an available bus, it begins transmitting the message
which has been determined to have the highest priority.
enqueued for transmission. When the module detects
an available bus, it begins transmitting the message
which has been determined to have the highest priority.
If the transmission completes successfully on the first
attempt, the TXREQ bit is cleared automatically and an
interrupt is generated if TXIE was set.
attempt, the TXREQ bit is cleared automatically and an
interrupt is generated if TXIE was set.
If the message transmission fails, one of the error
condition flags will be set and the TXREQ bit will
remain set indicating that the message is still pending
for transmission. If the message encountered an error
condition during the transmission attempt, the TXERR
bit will be set and the error condition may cause an
interrupt. If the message loses arbitration during the
transmission attempt, the TXLARB bit is set. No
interrupt is generated to signal the loss of arbitration.
condition flags will be set and the TXREQ bit will
remain set indicating that the message is still pending
for transmission. If the message encountered an error
condition during the transmission attempt, the TXERR
bit will be set and the error condition may cause an
interrupt. If the message loses arbitration during the
transmission attempt, the TXLARB bit is set. No
interrupt is generated to signal the loss of arbitration.
19.5.4
ABORTING MESSAGE
TRANSMISSION
TRANSMISSION
The system can also abort a message by clearing the
TXREQ bit associated with each message buffer.
Setting the ABAT bit (CiCTRL<12>) will request an
abort of all pending messages. If the message has not
yet started transmission, or if the message started but
is interrupted by loss of arbitration or an error, the abort
will be processed. The abort is indicated when the
module sets the TXABT bit, and the TXnIF flag is not
automatically set.
TXREQ bit associated with each message buffer.
Setting the ABAT bit (CiCTRL<12>) will request an
abort of all pending messages. If the message has not
yet started transmission, or if the message started but
is interrupted by loss of arbitration or an error, the abort
will be processed. The abort is indicated when the
module sets the TXABT bit, and the TXnIF flag is not
automatically set.
19.5.5
TRANSMISSION ERRORS
The CAN module will detect the following transmission
errors:
errors:
• Acknowledge error
• Form error
• Bit error
These transmission errors will not necessarily generate
an interrupt, but are indicated by the transmission error
counter. However, each of these errors will cause the
transmission error counter to be incremented by one.
Once the value of the error counter exceeds the value
of 96, the ERRIF (CiINTF<5>) and the TXWAR bit
(CiINTF<10>) are set. Once the value of the error
counter exceeds the value of 96, an interrupt is
generated and the TXWAR bit in the Error Flag register
is set.
an interrupt, but are indicated by the transmission error
counter. However, each of these errors will cause the
transmission error counter to be incremented by one.
Once the value of the error counter exceeds the value
of 96, the ERRIF (CiINTF<5>) and the TXWAR bit
(CiINTF<10>) are set. Once the value of the error
counter exceeds the value of 96, an interrupt is
generated and the TXWAR bit in the Error Flag register
is set.