MC9S08DZ96F2CLL datasheet(301/458 Pages) FREESCALE

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Chapter 12 Freescale’s Controller Area Network (S08MSCANV1)

MC9S08DZ128 Series Data Sheet, Rev. 1

Freescale Semiconductor

301

12.5.5.5

MSCAN Initialization Mode

In initialization mode, any on-going transmission or reception is immediately aborted and synchronization

to the CAN bus is lost, potentially causing CAN protocol violations. To protect the CAN bus system from

fatal consequences of violations, the MSCAN immediately drives the TXCAN pin into a recessive state.

NOTE

The user is responsible for ensuring that the MSCAN is not active when

initialization mode is entered. The recommended procedure is to bring the

MSCAN into sleep mode (SLPRQ = 1 and SLPAK = 1) before setting the

INITRQ bit in the CANCTL0 register. Otherwise, the abort of an on-going

message can cause an error condition and can impact other CAN bus

devices.

In initialization mode, the MSCAN is stopped. However, interface registers remain accessible. This mode

is used to reset the CANCTL0, CANRFLG, CANRIER, CANTFLG, CANTIER, CANTARQ,

CANTAAK, and CANTBSEL registers to their default values. In addition, the MSCAN enables the

conﬁguration of the CANBTR0, CANBTR1 bit timing registers; CANIDAC; and the CANIDAR,

CANIDMR message ﬁlters. See Section 12.3.1, “MSCAN Control Register 0 (CANCTL0),” for a detailed

description of the initialization mode.

Figure 12-46. Initialization Request/Acknowledge Cycle

Due to independent clock domains within the MSCAN, INITRQ must be synchronized to all domains by

using a special handshake mechanism. This handshake causes additional synchronization delay (see

Section Figure 12-46., “Initialization Request/Acknowledge Cycle”).

If there is no message transfer ongoing on the CAN bus, the minimum delay will be two additional bus

clocks and three additional CAN clocks. When all parts of the MSCAN are in initialization mode, the

INITAK ﬂag is set. The application software must use INITAK as a handshake indication for the request

(INITRQ) to go into initialization mode.

NOTE

The CPU cannot clear INITRQ before initialization mode (INITRQ = 1 and

INITAK = 1) is active.

SYNC

Bus Clock Domain

CAN Clock Domain

CPU

Init Request

INIT

Flag

INITAK

Flag

INITRQ

sync.

INITAK

sync.

INITRQ

INITAK

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