MC9S08DZ96F2CLL datasheet(296/458 Pages) FREESCALE

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Chapter 12 Freescale’s Controller Area Network (S08MSCANV1)

MC9S08DZ128 Series Data Sheet, Rev. 1

296

Freescale Semiconductor

12.5.4.3

Emulation Modes

In all emulation modes, the MSCAN module behaves just like normal system operation modes as

described within this speciﬁcation.

12.5.4.4

Listen-Only Mode

In an optional CAN bus monitoring mode (listen-only), the CAN node is able to receive valid data frames

and valid remote frames, but it sends only “recessive” bits on the CAN bus. In addition, it cannot start a

transmision. If the MAC sub-layer is required to send a “dominant” bit (ACK bit, overload ﬂag, or active

error ﬂag), the bit is rerouted internally so that the MAC sub-layer monitors this “dominant” bit, although

the CAN bus may remain in recessive state externally.

12.5.4.5

Security Modes

The MSCAN module has no security features.

12.5.4.6

Loopback Self Test Mode

Loopback self test mode is sometimes used to check software, independent of connections in the external

system, to help isolate system problems. In this mode, the transmitter output is internally connected to the

receiver input. The RXCAN input pin is ignored and the TXCAN output goes to the recessive state (logic

1). The MSCAN behaves as it does normally when transmitting and treats its own transmitted message as

a message received from a remote node. In this state, the MSCAN ignores the bit sent during the ACK slot

in the CAN frame acknowledge ﬁeld to ensure proper reception of its own message. Both transmit and

receive interrupts are generated.

12.5.5

Low-Power Options

If the MSCAN is disabled (CANE = 0), the MSCAN clocks are stopped for power saving.

If the MSCAN is enabled (CANE = 1), the MSCAN has two additional modes with reduced power

consumption, compared to normal mode: sleep and power down mode. In sleep mode, power consumption

is reduced by stopping all clocks except those to access the registers from the CPU side. In power down

mode, all clocks are stopped and no power is consumed.

Table 12-36 summarizes the combinations of MSCAN and CPU modes. A particular combination of

modes is entered by the given settings on the CSWAI and SLPRQ/SLPAK bits.

For all modes, an MSCAN wake-up interrupt can occur only if the MSCAN is in sleep mode (SLPRQ = 1

and SLPAK = 1), wake-up functionality is enabled (WUPE = 1), and the wake-up interrupt is enabled

(WUPIE = 1).

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