P912XDP512F0MPVR datasheet(474/1348 Pages) FREESCALE

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

MC9S12XDP512 Data Sheet, Rev. 2.21

474

Freescale Semiconductor

(CANTFLG).” Interrupts are pending as long as one of the corresponding ﬂags is set. The ﬂags in

CANRFLG and CANTFLG must be reset within the interrupt handler to handshake the interrupt. The ﬂags

are reset by writing a 1 to the corresponding bit position. A ﬂag cannot be cleared if the respective

condition prevails.

NOTE

It must be guaranteed that the CPU clears only the bit causing the current

interrupt. For this reason, bit manipulation instructions (BSET) must not be

used to clear interrupt ﬂags. These instructions may cause accidental

clearing of interrupt ﬂags which are set after entering the current interrupt

service routine.

10.4.7.7

Recovery from Stop or Wait

The MSCAN can recover from stop or wait via the wake-up interrupt. This interrupt can only occur if the

MSCAN was in sleep mode (SLPRQ = 1 and SLPAK = 1) before entering power down mode, the wake-up

option is enabled (WUPE = 1), and the wake-up interrupt is enabled (WUPIE = 1).

10.5

Initialization/Application Information

10.5.1

MSCAN initialization

The procedure to initially start up the MSCAN module out of reset is as follows:

1. Assert CANE

2. Write to the conﬁguration registers in initialization mode

3. Clear INITRQ to leave initialization mode and enter normal mode

If the conﬁguration of registers which are writable in initialization mode needs to be changed only when

the MSCAN module is in normal mode:

1. Bring the module into sleep mode by setting SLPRQ and awaiting SLPAK to assert after the CAN

bus becomes idle.

2. Enter initialization mode: assert INITRQ and await INITAK

3. Write to the conﬁguration registers in initialization mode

4. Clear INITRQ to leave initialization mode and continue in normal mode

10.5.2

Bus-Off Recovery

The bus-off recovery is user conﬁgurable. The bus-off state can either be left automatically or on user

request.

For reasons of backwards compatibility, the MSCAN defaults to automatic recovery after reset. In this

case, the MSCAN will become error active again after counting 128 occurrences of 11 consecutive

recessive bits on the CAN bus (See the Bosch CAN speciﬁcation for details).

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