PIC18F6680-I/L Microchip Technology, PIC18F6680-I/L Datasheet - Page 335

• Manufacturer Part Number: PIC18F6680-I/L
• Description: Microcontrollers (MCU) 64KB 3328 RAM 52 I/O
• Manufacturer: Microchip Technology

Specifications of PIC18F6680-I/L

• Processor Series: PIC18F
• Core: PIC
• Data Bus Width: 8 bit
• Data Ram Size: 3.25 KB
• Interface Type: I2C/SPI/AUSART/CAN
• Maximum Clock Frequency: 40 MHz
• Number Of Programmable I/os: 53
• Number Of Timers: 5
• Operating Supply Voltage: 4.2 V to 5.5 V
• Maximum Operating Temperature: + 85 C
• Mounting Style: SMD/SMT
• 3rd Party Development Tools: 52715-96, 52716-328, 52717-734, 52712-325, EWPIC18
• Development Tools By Supplier: PG164130, DV164035, DV244005, DV164005, PG164120, ICE2000, ICE4000, DV164136
• Minimum Operating Temperature: - 40 C
• On-chip Adc: 12-ch x 10-bit
• Program Memory Type: Flash
• Program Memory Size: 64 KB
• Package / Case: PLCC-68
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

23.7
23.7.1
Of all receive buffers, the MAB is always committed to
receiving the next message from the bus. The MCU
can access one buffer while the other buffer is available
for message reception, or holding a previously received
message.
When a message is moved into either of the receive
buffers, the associated RXFUL bit is set. This bit must
be cleared by the MCU when it has completed process-
ing 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 firmware
has finished with the message before the module
attempts to load a new message into the receive buffer.
If the receive interrupt is enabled, an interrupt will be
generated to indicate that a valid message has been
received.
Once a message is loaded into any matching buffer,
user firmware may determine exactly what filter caused
this reception by checking the filter hit bits in the
RXBnCON or BnCON registers. In Mode 0, FILHIT<3:0>
of RXBnCON serve as filter hit bits. In Mode 1 and 2,
FILHIT<4:0> of BnCON serve as filter hit bits. The same
registers also indicate whether the current message is
RTR frame or not. A received message is considered a
standard identifier message if the EXID bit in RXBnSIDL
or the BnSIDL register is cleared. Conversely, a set
EXID bit indicates an extended identifier message. If the
received message is a standard identifier message, user
firmware needs to read the SIDL and SIDH registers. In
the case of an extended identifier message, firmware
should read the SIDL, SIDH, EIDL and EIDH registers. If
the RXBnDLC or BnDLC register contain non-zero data
count, user firmware should also read the corresponding
number of data bytes by accessing the RXBnDm or
BnDm registers. When a received message is RTR and
if the current buffer is not configured for automatic RTR
handling, user firmware must take appropriate action
and respond manually.
 2004 Microchip Technology Inc.
Note:
Message Reception
RECEIVING A MESSAGE
The entire contents of the MAB are moved
into the receive buffer once a message is
accepted. This means that regardless of
the
extended) and the number of data bytes
received, the entire receive buffer is over-
written with the MAB contents. Therefore,
the contents of all registers in the buffer
must be assumed to have been modified
when any message is received.
type
of
identifier
(standard
PIC18F6585/8585/6680/8680
or
Each receive buffer contains RXM bits to set special
Receive modes. In Mode 0, RXM<1:0> bits in
RXBnCON define a total of four Receive modes. In
Mode 1 and 2, RXM1 bit in combination with the EXID
mask and filter bit define the same four Receive
modes. 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 deter-
mination of whether or not to receive standard or
extended messages is determined by the EXIDE bit in
the Acceptance Filter register. In Mode 0, if the RXM
bits are set to ‘01’ or ‘10’, the receiver will accept only
messages with standard or extended identifiers,
respectively. If an acceptance filter has the EXIDE bit
set such that it does not correspond with the RXM
mode, that acceptance filter is rendered useless. In
Mode 1 and 2, setting EXID in the SIDL Mask register
will ensure that only standard or extended identifiers
are received. These two modes of RXM bits can be
used in systems where it is known that only standard or
extended messages will be on the bus. If the RXM bits
are set to ‘11’ (RXM1 = 1 in Mode 1 and 2), the buffer
will 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 may serve as a valu-
able debugging tool for a given CAN network. It should
not be used in an actual system environment as the
actual system will always have some bus errors and all
nodes on the bus are expected to ignore them.
In Mode 1 and 2, when a programmable buffer is
configured as a transmit buffer and one or more accep-
tance filters are associated with it, all incoming mes-
sages matching this acceptance filter criteria will be
discarded. To avoid this scenario, user firmware must
make sure that there are no acceptance filters associ-
ated with a buffer configured as a transmit buffer.
23.7.2
When in Mode 0, 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 associated 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
RXB0CON 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 regardless of the
acceptance criteria of RXB1. There are also two
programmable acceptance filter masks available, one for
each receive buffer (see Section 4.5).
RECEIVE PRIORITY
DS30491C-page 333