MCP2510-ESO MICROCHIP [Microchip Technology], MCP2510-ESO Datasheet - Page 21

• Manufacturer Part Number: MCP2510-ESO
• Description: Stand-Alone CAN Controller with SPI Interface
• Manufacturer: MICROCHIP [Microchip Technology]

4.0
4.1
The MCP2510 includes two full receive buffers with
multiple acceptance filters for each. There is also a
separate Message Assembly Buffer (MAB) which acts
as a third receive buffer (see Figure 4-1).
4.2
Of the three Receive Buffers, the MAB is always com-
mitted to receiving the next message from the bus. The
remaining two receive buffers are called RXB0 and
RXB1 and can receive a complete message from the
protocol engine. The MCU can access one buffer while
the other buffer is available for message reception or
holding a previously received message.
The MAB assembles all messages received. These
messages will be transferred to the RXB
Register 4-4 to Register 4-9) only if the acceptance fil-
ter criteria are met.
When a message is moved into either of the receive
buffers the appropriate CANINTF.RX
bit must be cleared by the MCU, when it has completed
processing the message in the buffer, in order to allow
a new message to be received into the buffer. This bit
provides a positive lockout to ensure that the MCU has
finished with the message before the MCP2510
attempts to load a new message into the receive buffer.
If the CANINTE.RX
erated on the INT pin to indicate that a valid message
has been received.
4.3
RXB0 is the higher priority buffer and has two message
acceptance filters associated with it. RXB1 is the lower
priority buffer and has four acceptance filters associ-
ated with it. The lower number of acceptance filters
makes the match on RXB0 more restrictive and implies
a higher priority for that buffer. Additionally, the
RXB0CTRL register can be configured such that if
RXB0 contains a valid message, and another valid
message is received, an overflow error will not occur
and the new message will be moved into RXB1 regard-
less of the acceptance criteria of RXB1. There are also
two programmable acceptance filter masks available,
one for each receive buffer (see Section 4.5).
Note: The entire contents of the MAB is moved into
2000 Microchip Technology Inc.
MESSAGE RECEPTION
Receive Message Buffering
Receive Buffers
the receive buffer once a message is
accepted. This means that regardless of the
type of identifier (standard or extended) and
the number of data bytes received, the entire
receive buffer is overwritten with the MAB
contents. Therefore the contents of all regis-
ters in the buffer must be assumed to have
been modified when any message is
received.
Receive Priority
N
IE bit is set an interrupt will be gen-
N
IF bit is set. This
N
buffers (See
Preliminary
When a message is received, bits <3:0> of the RXB
Register will indicate the acceptance filter number that
enabled reception, and whether the received message is a
remote transfer request.
The RXB
Normally, these bits are set to 00 to enable reception of
all valid messages as determined by the appropriate
acceptance filters. In this case, the determination of
whether or not to receive standard or extended mes-
sages is determined by the RFX
acceptance filter register. If the RXB
are set to 01 or 10, the receiver will accept only mes-
sages with standard or extended identifiers respec-
tively. If an acceptance filter has the RFX
bit set such that it does not correspond with the
RXB
dered useless. These two modes of RXB
bits can be used in systems where it is known that only
standard or extended messages will be on the bus. If
the RXB
receive all messages regardless of the values of the
acceptance filters. Also, if a message has an error
before the end of frame, that portion of the message
assembled in the MAB before the error frame will be
loaded into the buffer. This mode has some value in
debugging a CAN system and would not be used in an
actual system environment.
4.4
In addition to the INT pin which provides an interrupt
signal to the MCU for many different conditions, the
receive buffer full pins (RX0BF and RX1BF) can be
used to indicate that a valid message has been loaded
into RXB0 or RXB1, respectively.
The RXB
full interrupt pins or as standard digital outputs. Config-
uration and status of these pins is available via the
BFPCTRL register (Register 4-3). When set to operate
in interrupt mode (by setting BFPCTRL.BxBFE and
BFPCTRL.BxBFM bits to a 1), these pins are active low
and are mapped to the CANINTF.RX
receive buffer. When this bit goes high for one of the
receive buffers, indicating that a valid message has
been loaded into the buffer, the corresponding RX
pin will go low. When the CANINTF.RX
by the MCU, then the corresponding interrupt pin will
go to the logic high state until the next message is
loaded into the receive buffer.
When used as digital outputs the BFPCTRL.BxBFM
and BFPCTRL.BxBFE bits must be set to a ‘1’ for the
associated buffer. In this mode the state of the pin is
controlled by the BFPCTRL.BxBFS bits. Writting a ‘1’
to the BxBFS bit will cause a high level to be driven on
the assicated buffer full pin, and a ‘0’ will cause the pin
to drive low. When using the pins in this mode the state
of the pin should be modified only by using the Bit Mod-
ify SPI command to prevent glitches from occuring on
either of the buffer full pins.
N
CTRL.RXM mode, that acceptance filter is ren-
N
RX0BF and RX1BF Pins
N
N
CTRL.RXM bits are set to 11, the buffer will
BF full pins can be configured to act as buffer
CTRL.RXM bits set special receive modes.
MCP2510
N
SIDL.EXIDE bit in the
DS21291C-page 21
N
N
N
CTRL.RXM bits
IF bit is cleared
IF bit for each
N
N
SIDL.EXIDE
CTRL.RXM
N
CTRL
N
BF