Datasheet

Programmer’s Model of Message Storage
MC68HC908GZ16 • MC68HC908GZ8 Data Sheet, Rev. 4
Freescale Semiconductor 139
12.12.2 Identifier Registers
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 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 case of a transmit buffer, the flag indicates to the MSCAN08 what type of
identifier to send.
1 = Extended format, 29 bits
0 = Standard format, 11 bits
RTR — Remote Transmission Request
This flag reflects the status of the remote transmission request bit in the CAN frame. In case of a
receive buffer, it indicates the status of the received frame and supports the transmission of an
answering frame in software. In case of a transmit buffer, this flag defines the setting of the RTR bit to
be sent.
1 = Remote frame
0 = Data frame
Addr. Register Bit 7 6 5 4 3 2 1 Bit 0
$05b0 IDR0
Read:
ID10 ID9 ID8 ID7 ID6 ID5 ID4 ID3
Write:
$05b1 IDR1
Read:
ID2 ID1 ID0 RTR IDE (=0)
Write:
$05b2 IDR2
Read:
Write:
$05b3 IDR3
Read:
Write:
= Unimplemented
Figure 12-13. Standard Identifier Mapping