DSPIC30F5011-20I/PTG Microchip Technology, DSPIC30F5011-20I/PTG Datasheet - Page 112

• Manufacturer Part Number: DSPIC30F5011-20I/PTG
• Description: IC, DSC, 16BIT, 66KB, 40MHZ 5.5V TQFP-64
• Manufacturer: Microchip Technology
• Series: DsPIC30Fr

Specifications of DSPIC30F5011-20I/PTG

• Core Frequency: 40MHz
• Core Supply Voltage: 5.5V
• Embedded Interface Type: CAN, I2C, SPI, UART
• No. Of I/o's: 52
• Flash Memory Size: 66KB
• Supply Voltage Range: 2.5V To 5.5V
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

dsPIC30F5011/5013
17.4
17.4.1
The CAN bus module has 3 receive buffers. However,
one of the receive buffers is always committed to
monitoring the bus for incoming messages. This buffer
is called the Message Assembly Buffer (MAB). 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
transferred to the RXBn buffers only if the acceptance
filter criterion are met. When a message is received, the
RXnIF flag (CiINTF<0> or CiINRF<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 processing the message in the buffer. If the
RXnIE bit (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.
17.4.2
The message acceptance filters and masks are used to
determine if a message in the message assembly
buffer should be loaded into either of the receive
buffers. Once a valid message has been received into
the MAB, the identifier fields of the message 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.
17.4.3
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.
DS70116H-page 112
Message Reception
RECEIVE BUFFERS
MESSAGE ACCEPTANCE FILTERS
MESSAGE ACCEPTANCE FILTER
MASKS
instantaneously
receive
a
complete
17.4.4
An overrun condition occurs when the MAB has
assembled a valid received message, the message is
accepted through the acceptance filters and when the
receive buffer associated with the filter has not been
designated as clear of the previous message.
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
independently. 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, indicating that both RXB0 and
RXB1 are full, the message will be lost and an overrun
will be indicated for RXB1.
17.4.5
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.
17.4.6
Receive interrupts can be divided into 3 major groups,
each including various conditions that generate
interrupts:
• Receive Interrupt:
• Wake-up Interrupt:
A message has been successfully received and
loaded into one of the receive buffers. This
interrupt is activated immediately after receiving
the End-of-Frame (EOF) field. Reading the RXnIF
flag will indicate which receive buffer caused the
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
© 2008 Microchip Technology Inc.