Freescale’s Scalable Controller Area Network (S12MSCANV3)
8.3.3.3
Data Length Register (DLR)
This register keeps the data length field of the CAN frame.
Module Base + 0x00XC
7
6
5
4
3
2
1
0
R
W
DLC3
DLC2
DLC1
DLC0
Reset:
x
x
x
x
x
x
x
x
= Unused; always read “x”
Figure 8-35. Data Length Register (DLR) — Extended Identifier Mapping
Table 8-34. DLR Register Field Descriptions
Description
Field
3-0
DLC[3:0]
Data Length Code Bits — The data length code contains the number of bytes (data byte count) of the respective
message. During the transmission of a remote frame, the data length code is transmitted as programmed while
the number of transmitted data bytes is always 0. The data byte count ranges from 0 to 8 for a data frame.
Table 8-35 shows the effect of setting the DLC bits.
Table 8-35. Data Length Codes
Data Length Code
Data Byte
Count
DLC3
DLC2
DLC1
DLC0
0
0
0
0
0
0
0
0
1
0
0
0
0
1
1
1
1
0
0
0
1
1
0
0
1
1
0
0
1
0
1
0
1
0
1
0
0
1
2
3
4
5
6
7
8
8.3.3.4
Transmit Buffer Priority Register (TBPR)
This register defines the local priority of the associated message buffer. The local priority is used for the
internal prioritization process of the MSCAN and is defined to be highest for the smallest binary number.
The MSCAN implements the following internal prioritization mechanisms:
•
All transmission buffers with a cleared TXEx flag participate in the prioritization immediately
before the SOF (start of frame) is sent.
•
The transmission buffer with the lowest local priority field wins the prioritization.
S12P-Family Reference Manual, Rev. 1.13
Freescale Semiconductor
283
FREESCALE [ Freescale ]
