MSCAN Controller
Programmer’s Model of Message Storage
68HC(9)12DG128 Rev 1.0
MOTOROLA
MSCAN Controller
311
25-mscan12
Identifier Registers
(IDRn)
The identifiers consist of either 11 bits (ID10–ID0) for the standard, or 29
bits (ID28–ID0) for the extended format. ID10/28 is the most significant
bit and is transmitted first on the bus during the arbitration procedure.
The priority of an identifier is defined to be highest for the smallest binary
number.
SRR — Substitute Remote Request
This fixed recessive bit is used only in extended format. It must be set
to 1 by the user for transmission buffers and will be stored as received
on the CAN bus for receive buffers.
IDE — ID Extended
This flag indicates whether the extended or standard identifier format
is applied in this buffer. In the case of a receive buffer the flag is set
as being received and indicates to the CPU how to process the buffer
identifier registers. In the case of a transmit buffer the flag indicates to
the msCAN12 what type of identifier to send.
0 = Standard format (11-bit)
1 = Extended format (29-bit)
RTR — Remote transmission request
This flag reflects the status of the Remote Transmission Request bit
in the CAN frame. In the case of a receive buffer it indicates the status
of the received frame and supports the transmission of an answering
frame in software. In the case of a transmit buffer, this flag defines the
setting of the RTR bit to be sent.
0 = Data frame
1 = Remote frame
Data Length
Register (DLR)
This register 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 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 44
shows the effect of setting the DLC
bits.