MC68HC908AT32 Datasheet, PDF (267/378 Pages) Freescale Semiconductor, Inc – Microcontrollers

Programmer’s Model of Message Storage
23.12.3 Data Length Register
The data length register (DLR) keeps the data length field of the CAN frame.
DLC3–DLC0 — Data Length Code Bits
The data length code contains the number of bytes (data byte count) of the respective message. At
transmission of a remote frame, the data length code is transmitted as programmed while the number
of transmitted bytes is always 0. The data byte count ranges from 0 to 8 for a data frame. Table 23-3
shows the effect of setting the DLC bits.
Table 23-3. Data Length Codes
DLC3
0
0
0
0
0
0
0
0
1
Data Length Code
DLC2 DLC1
0
0
0
0
0
1
0
1
1
0
1
0
1
1
1
1
0
0
DLC0
0
1
0
1
0
1
0
1
0
Data Byte
Count
0
1
2
3
4
5
6
7
8
23.12.4 Data Segment Registers
The eight data segment registers (DSRn) contain the data to be transmitted or received. The number of
bytes to be transmitted
or being received is determined by the data length code in the corresponding DLR.
23.12.5 Transmit Buffer Priority Registers
Address:
Read:
Write:
Reset:
$05bD
Bit 7
6
5
4
3
2
1
PRIO7 PRIO6 PRIO5 PRIO4 PRIO3 PRIO2 PRIO1
0
0
0
0
0
0
0
Figure 23-12. Transmit Buffer Priority Register (TBPR)
Bit 0
PRIO0
0
PRIO7–PRIO0 — Local Priority Field
This field defines the local priority of the associated message buffer. The local priority is used for the
internal prioritization process of the MSCAN08 and is defined to be highest for the smallest binary
number. The MSCAN08 implements the following internal prioritization mechanism:
• All transmission buffers with a cleared TXE flag participate in the priorization right before the SOF
is sent.
• The transmission buffer with the lowest local priority field wins the prioritization.
• In case more than one buffer has the same lowest priority, the message buffer with the lower index
number wins.
MC68HC908AT32 Data Sheet, Rev. 3.1
Freescale Semiconductor
267