DSPIC30F6010A MICROCHIP [Microchip Technology], DSPIC30F6010A Datasheet - Page 130

• Manufacturer Part Number: DSPIC30F6010A
• Description: High-Performance, 16-bit Digital Signal Controllers
• Manufacturer: MICROCHIP [Microchip Technology]

processing the message in the buffer. If the RXnIE bit
dsPIC30F6010A/6015
19.4
19.4.1
The CAN bus module has 3 receive buffers. However,
one of the receive buffers is always committed to mon-
itoring the bus for incoming messages. This buffer is
called the Message Assembly Buffer (MAB). So there
are 2 receive buffers visible, RXB0 and RXB1, that can
essentially
message from the protocol engine.
All messages are assembled by the MAB, and are trans-
ferred to the RXBn buffers only if the acceptance filter
criterion is met. When a message is received, the RXnIF
flag (CiINTF<0> or CiINTF<1>) will be set. This bit can
only be set by the module when a message is received.
The bit is cleared by the CPU when it has completed
(CiINTE<0> or CiINTE<1>) is set, an interrupt will be
generated when a message is received.
RXF0 and RXF1 filters with RXM0 mask are associated
with RXB0. The filters RXF2, RXF3, RXF4, and RXF5
and the mask RXM1 are associated with RXB1.
19.4.2
The message acceptance filters and masks are used to
determine if a message in the message assembly buf-
fer should be loaded into either of the receive buffers.
Once a valid message has been received into the mes-
sage assembly buffer, the identifier fields of the mes-
sage are compared to the filter values. If there is a
match, that message will be loaded into the appropriate
receive buffer.
The acceptance filter looks at incoming messages for
the RXIDE bit (CiRXnSID<0>) to determine how to
compare the identifiers. If the RXIDE bit is clear, the
message is a standard frame, and only filters with the
EXIDE bit (CiRXFnSID<0>) clear are compared. If the
RXIDE bit is set, the message is an extended frame,
and only filters with the EXIDE bit set are compared.
Configuring the RXM<1:0> bits to ‘01’ or ‘10’ can
override the EXIDE bit.
19.4.3
The mask bits essentially determine which bits to apply
the filter to. If any mask bit is set to a zero, then that bit
will automatically be accepted regardless of the filter
bit. There are 2 programmable acceptance filter masks
associated with the receive buffers, one for each buffer.
DS70150E-page 130
Message Reception
RECEIVE BUFFERS
MESSAGE ACCEPTANCE FILTERS
MESSAGE ACCEPTANCE FILTER
MASKS
instantaneously
receive
a
complete
19.4.4
An overrun condition occurs when the message
assembly buffer has assembled a valid received
message and the message is accepted through the
acceptance filters, but the receive buffer associated
with the filter still contains unread data.
The overrun error flag, RXnOVR (CiINTF<15> or
CiINTF<14>) and the ERRIF bit (CiINTF<5>) will be set
and the message in the MAB will be discarded.
If the DBEN bit is clear, RXB1 and RXB0 operate inde-
pendently. When this is the case, a message intended
for RXB0 will not be diverted into RXB1 if RXB0
contains an unread message and the RX0OVR bit will
be set.
If the DBEN bit is set, the overrun for RXB0 is handled
differently. If a valid message is received for RXB0 and
RXFUL = 1 indicates that RXB0 is full and RXFUL = 0
indicates that RXB1 is empty, the message for RXB0
will be loaded into RXB1. An overrun error will not be
generated for RXB0. If a valid message is received for
RXB0 and RXFUL = 1, and RXFUL = 1 indicating that
both RXB0 and RXB1 are full, the message will be lost
and an overrun will be indicated for RXB1.
19.4.5
The CAN module will detect the following receive
errors:
• Cyclic Redundancy Check (CRC) error
• Bit Stuffing error
• Invalid message receive error
The receive error counter is incremented by one in
case one of these errors occur. The RXWAR bit
(CiINTF<9>) indicates that the Receive Error Counter
has reached the CPU warning limit of 96 and an
interrupt is generated.
19.4.6
Receive interrupts can be divided into 3 major groups,
each including various conditions that generate
interrupts:
• Receive Interrupt
A message has been successfully received and loaded
into one of the receive buffers. This interrupt is acti-
vated immediately after receiving the End-of-Frame
(EOF) field. Reading the RXnIF flag will indicate which
receive buffer caused the interrupt.
• Wake-up Interrupt
The CAN module has woken up from Disable mode or
the device has woken up from Sleep mode.
RECEIVE OVERRUN
RECEIVE ERRORS
RECEIVE INTERRUPTS
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