MC908AZ60ACFUER Datasheet, PDF (270/414 Pages) Freescale Semiconductor, Inc – To provide the most up-to-date information, the revision of our documents on the World Wide Web will be the most current. Your printed copy may be an earlier revision. To verify you have the latest information available, refer to:

MSCAN Controller (MSCAN08)
An overrun condition occurs when both the foreground and the background receive message buffers are
filled with correctly received messages with accepted identifiers and another message is correctly
received from the bus with an accepted identifier. The latter message will be discarded and an error
interrupt with overrun indication will be generated if enabled. The MSCAN08 is still able to transmit
messages with both receive message buffers filled, but all incoming messages are discarded.
MSCAN08
CPU08 Ibus
RxBG
RxFG
RXF
Tx0
TXE
PRIO
Tx1
TXE
PRIO
Tx2
TXE
PRIO
Figure 23-2. User Model for Message Buffer Organization
23.4.3 Transmit Structures
The MSCAN08 has a triple transmit buffer scheme to allow multiple messages to be set up in advance
and to achieve an optimized real-time performance. The three buffers are arranged as shown in Figure
23-2.
All three buffers have a 13-byte data structure similar to the outline of the receive buffers (see 23.12
Programmer’s Model of Message Storage). An additional transmit buffer priority register (TBPR) contains
an 8-bit “local priority” field (PRIO) (see 23.12.5 Transmit Buffer Priority Registers).
MC68HC908AZ60A • MC68HC908AS60A • MC68HC908AS60E Data Sheet, Rev. 6
270
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