P912XDP512F0MPVR datasheet(455/1348 Pages) FREESCALE

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Chapter 10 Freescale’s Scalable Controller Area Network (S12MSCANV3)

MC9S12XDP512 Data Sheet, Rev. 2.21

Freescale Semiconductor

455

10.3.3.4

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.

In cases of more than one buffer having the same lowest priority, the message buffer with the lower index

number wins.

Read: Anytime when TXEx ﬂag is set (see Section 10.3.2.7, “MSCAN Transmitter Flag Register

(CANTFLG)”) and the corresponding transmit buffer is selected in CANTBSEL (see Section 10.3.2.11,

“MSCAN Transmit Buffer Selection Register (CANTBSEL)”).

Write: Anytime when TXEx ﬂag is set (see Section 10.3.2.7, “MSCAN Transmitter Flag Register

(CANTFLG)”) and the corresponding transmit buffer is selected in CANTBSEL (see Section 10.3.2.11,

“MSCAN Transmit Buffer Selection Register (CANTBSEL)”).

10.3.3.5

Time Stamp Register (TSRH–TSRL)

If the TIME bit is enabled, the MSCAN will write a time stamp to the respective registers in the active

transmit or receive buffer right after the EOF of a valid message on the CAN bus (see Section 10.3.2.1,

Table 10-33. Data Length Codes

Data Length Code

Data Byte

Count

DLC3

DLC2

DLC1

DLC0

0000

0001

0010

0011

0100

0101

0110

0111

1000

76543210

PRIO7

PRIO6

PRIO5

PRIO4

PRIO3

PRIO2

PRIO1

PRIO0

Reset:

00000000

Figure 10-36. Transmit Buffer Priority Register (TBPR)

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