Chapter 16 Freescale’s Scalable Controller Area Network (S12MSCANV3)
MC9S12XE-Family Reference Manual , Rev. 1.19
656
Freescale Semiconductor
•
CAN Status Change
— The actual value of the transmit and receive error counters control the
CAN bus state of the MSCAN. As soon as the error counters skip into a critical range (Tx/Rx-
warning, Tx/Rx-error, bus-off) the MSCAN flags an error condition. The status change, which
caused the error condition, is indicated by the TSTAT and RSTAT flags (see
“MSCAN Receiver Flag Register (CANRFLG)
Section 16.3.2.6, “MSCAN Receiver
Interrupt Enable Register (CANRIER)
16.4.7.6
Interrupt Acknowledge
Interrupts are directly associated with one or more status flags in either the
Receiver Flag Register (CANRFLG)
” or the
Section 16.3.2.7, “MSCAN Transmitter Flag Register
.” 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.
16.4.7.7
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).
16.5
Initialization/Application Information
16.5.1
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
Because
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Commission,
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