MSCAN08 Controller (MSCAN08)
MC68HC08GZ32 Data Sheet, Rev. 3
124
Freescale Semiconductor
12.7 Protocol Violation Protection
The MSCAN08 will protect the user from accidentally violating the CAN protocol through programming
errors. The protection logic implements the following features:
The receive and transmit error counters cannot be written or otherwise manipulated.
All registers which control the configuration of the MSCAN08 can not be modified while the
MSCAN08 is on-line. The SFTRES bit in the MSCAN08 module control register (see
12.13.1–
MSCAN08 module control register 1 (CMCR1)
–
MSCAN08 bus timing register 0 and 1 (CBTR0 and CBTR1)
–
MSCAN08 identifier acceptance control register (CIDAC)
–
MSCAN08 identifier acceptance registers (CIDAR0–3)
–
MSCAN08 identifier mask registers (CIDMR0–3)
The CANTX pin is forced to recessive when the MSCAN08 is in any of the low-power modes.
12.8 Low-Power Modes
In addition to normal mode, the MSCAN08 has three modes with reduced power consumption: sleep, soft
reset, and power down. In sleep and soft reset mode, power consumption is reduced by stopping all
clocks except those to access the registers. In power-down mode, all clocks are stopped and no power
is consumed.
The WAIT and STOP instructions put the MCU in low-power consumption stand-by modes.
Table 12-2summarizes the combinations of MSCAN08 and CPU modes. A particular combination of modes is
entered for the given settings of the bits SLPAK and SFTRES. For all modes, an MSCAN08 wakeup
interrupt can occur only if SLPAK = WUPIE = 1.
.
12.8.1 MSCAN08 Sleep Mode
The CPU can request the MSCAN08 to enter the low-power mode by asserting the SLPRQ bit in the
module configuration register (see
Figure 12-7). The time when the MSCAN08 enters sleep mode
depends on its activity:
If it is transmitting, it continues to transmit until there is no more message to be transmitted, and
then goes into sleep mode
If it is receiving, it waits for the end of this message and then goes into sleep mode
If it is neither transmitting or receiving, it will immediately go into sleep mode
Table 12-2. MSCAN08 versus CPU Operating Modes
MSCAN08 Mode
CPU Mode
STOP
WAIT or RUN
Power Down
SLPAK = X(1)
SFTRES = X
1. ‘X’ means don’t care.
Sleep
SLPAK = 1
SFTRES = 0
Soft Reset
SLPAK = 0
SFTRES = 1
Normal
SLPAK = 0
SFTRES = 0